Next Article in Journal
Hydrochemical Characteristics and Dominant Controlling Factors of the Qujiang River Under Dual Natural–Anthropogenic Influences
Previous Article in Journal
Fabrication of Silver-Incorporated Zn-Al Layered Double Hydroxide: Characterization and Bromide-Adsorption Performance
Previous Article in Special Issue
Distribution Characteristics and Sources of Microplastics in Inland Wetland Ecosystem Soils
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Water
Volume 17
Issue 11
10.3390/w17111579
water-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Contrasting Microplastic Characteristics in Macroinvertebrates from Two Independent but Adjacent Rivers in Kruger National Park, South Africa

by
Purvance Shikwambana
1,2,*,
Llewellyn C. Foxcroft
3,4,
Hindrik Bouwman
2,
Judith Botha
3 and
Jonathan C. Taylor
2,5
1
Faculty of Agriculture and Natural Sciences, University of Mpumalanga, Mbombela 1200, South Africa
2
Unit for Environmental Sciences and Management, North-West University, Potchefstroom 2531, South Africa
3
Scientific Services, South African National Parks, Skukuza 1350, South Africa
4
Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Matieland, Stellenbosch 7602, South Africa
5
South African Institute for Aquatic Biodiversity, Makhanda 6140, South Africa
*
Author to whom correspondence should be addressed.
Water 2025, 17(11), 1579; https://doi.org/10.3390/w17111579
Submission received: 10 April 2025 / Revised: 9 May 2025 / Accepted: 14 May 2025 / Published: 23 May 2025
(This article belongs to the Special Issue Impact of Microplastics on Aquatic Ecosystems)
Browse Figures
Versions Notes

Abstract

:
Freshwater macroinvertebrates, often used as indicators of environmental quality for freshwater ecosystems, may be compromised by microplastics (MPs). We investigated MPs occurring in benthic filter feeder, predator, and grazer macroinvertebrates collected from the catchment-independent but adjacent Olifants and Sabie rivers of Kruger National Park as duplicates. We counted 369 MPs in 376 organisms (1.0 n/organism) with a mean of 8.8 n/organism, 8.5 n/organism, and 0.16 n/organism in filter feeders, predators, and grazers, respectively. Based on MP colour, size, and morphotype, significant differences in proportional compositions between predatorial macroinvertebrates and all other macroinvertebrates in both rivers preclude predatorial macroinvertebrates as a proxy indicator for the other macroinvertebrates. Proportional compositions of MP characteristics in macroinvertebrates differed in all respects between the two adjacent rivers, except for one aspect. Microplastic morphotypes occurred in equal proportions in macroinvertebrates of both rivers, suggesting biological selection based on morphotype but not MP colour or size. We found little evidence of trophic transfer between feeding guilds. Of the six polymer types observed (n = 50), butyl and chlorobutyl dominated. Waste mismanagement, single-use plastics, inefficient wastewater treatment plants, mining, and road transportation may be the major MP pollution sources that need mitigation. Microplastics in freshwater ecosystems of nature conservation areas need more attention due to high biodiversity that may be exposed.

1. Introduction

Aquatic plastic pollution and its impact on aquatic organisms is a global concern [1,2,3]. Plastic waste is exposed to changes in temperature, ultraviolet light breakdown, abrasion, and wind [4,5], eventually resulting in particles that are <5 mm in the longest dimension, which are then referred to as microplastics (MPs) [6,7]. In addition, manufactured microbeads (<1 mm) are often found in personal care products, detergents, and as abrasives in sandblasting. MP fibres, on the other hand, are shed from, inter alia, woven materials, fabrics, and ropes [8,9,10]. These MPs reach aquatic ecosystems by wind, illegal dumping, mismanaged solid waste, atmospheric fallout, stormwater runoff, and wastewater treatment plant (WWTP) effluents [10,11]
Current MP pollution recorded from aquatic ecosystems and organisms suggests that MP pollution is extensive [12,13]. Although plastic pollution is pervasive in aquatic systems [14], there are potential solutions to reduce MP pollution; for example, the reduction or banning of single-use plastics, monetary levies, banning microbeads in personal care and other products, and the increasing use of biodegradable bioplastics [15,16,17,18]. Additionally, conventional plastics biodegrade very slowly [19]. For instance, it may take 500 years for a high-density polyethylene bottle to completely decompose on land and 116 years in marine environments [20]. Therefore, the plastic debris and MPs already present in aquatic systems will persist for a long time.
Microplastic pollution is considered a threat to freshwater and marine organisms [21,22,23]. Initial studies on the impacts of plastics in aquatic environments highlighted that plastic could be a vector of accumulated persistent organic pollutants, such as polychlorinated biphenyls, to animals [24]. Also, plastic serves as a growth medium and substrate for diatoms, macroinvertebrates, and bacteria [25,26,27]. Macroinvertebrates are often used as aquatic ecological indicators [27]. However, research has confirmed that freshwater macroinvertebrates are affected by MPs [28,29]. Microplastic ingestion by aquatic organisms could result in reduced growth, impaired feeding, and delayed reproduction, affect gastric enzymes, intestinal barrier function, and dysbiosis of microbial composition, and even have significant negative effects on their abundance [5,30].
Although the spatial distribution and effects of MPs in marine environments are well documented, freshwater ecosystems receive increasing attention [11,13,14,31]. Freshwater organisms, such as tilapia fish, clams, and midges, for instance, are considered bioindicators of MP pollution [21,31,32].
Riverbed sediment is an important habitat for aquatic macroinvertebrates. The benthic macroinvertebrates have different habitats and are composed of different feeding guilds such as grazers, filter feeders, and predators [33,34]. Macroinvertebrates’ habitat and feeding preference will likely influence the numbers, morphotypes, and size ranges of MPs they ingest [3,35]. For instance, MPs between 25 and 200 µm are likely to be ingested by lower trophic level macroinvertebrates while grazing because these MPs are in the same size range as diatoms and other single-celled algae. Macroinvertebrate taxa such as clams (Corbiculidae), horseflies (Tabanidae), and midges (Chironomidae) could ingest MPs from the sediment. Predatorial macroinvertebrates, such as dragonfly nymphs (Gomphidae and Libellulidae), are likely to ingest MPs in the gut and/or be incorporated into the bodies of their prey. Additionally, bioavailable MPs that are ingested and/or incorporated by aquatic organisms could be transferred to animals at higher trophic levels [29,30,36], conceivably reaching top aquatic predators, such as crocodiles, and terrestrial fauna that feed on aquatic organisms [37].
Kruger National Park (KNP) is a protected area located in northeastern South Africa (Figure 1a). Five major rivers cross the park from east to west towards the Indian Ocean after flowing through settled, agricultural, and industrial land with many putative MP pollution sources [38,39]. Indeed, previous studies reported a significant difference in water and sediment MPs based on size, colour, and morphotype between the two rivers [40]. We sampled macroinvertebrates and water from two of these rivers, the Sabie and Olifants. These two rivers are adjacent but have independent catchments. The aims of this study were to (i) compare MP characteristic compositions in macroinvertebrate guilds from and between the two rivers, (ii) investigate if predatory macroinvertebrates could serve as a proxy for all macroinvertebrates, (iii) infer possible MP sources based on their polymer compositions, and (iv) identify possible mitigation measures that would better protect Kruger National Park.

2. Materials and Methods

2.1. Study Area

KNP is a semi-arid nature reserve located in the northeastern part of South Africa (Figure 1a). The two rivers that are the subject of this study have independent catchments and meander east to west through the centre (Olifants River) and south (Sabie River) of KNP [40,41,42]. The catchment of the Olifants River is 840 km long, with 89% of its river reach outside KNP. The Sabie River has a 189 km long catchment, with 37% of its river reach located outside KNP [43]. The rivers have different land use activities and catchment sizes. Land use activities along the Olifants include mining, agriculture, and forestry, whilst the Sabie River catchment has mainly agriculture and forestry [44]. Both rivers are proximate to a growing human population, especially the Olifants River [45]. Both rivers have putative MP sources, inter alia, mismanaged solid waste, WWTPs, traffic-related activities, and stormwater runoff [39,40]. Indeed, MPs have been identified in the water and bottom sediments of both rivers [40].

2.2. Macroinvertebrate Collection

Macroinvertebrate samples were collected during the KNP Annual River Eco-status Monitoring survey centred on designated water quality sampling sites (6–21 September 2018) (Figure 1b–f). Macroinvertebrate presence is habitat and water quality dependent [33]. For example, macroinvertebrates, such as Oligochaeta and Tabanidae, are found in muddy substrates in pools and quiet streams and not in rocky bottoms [33]. Macroinvertebrate samples were collected using the South African Scoring System (SASS) version 5 according to Dickens et al., 2010 [33], with minor modifications regarding unrestricted sample collection time. To obtain sufficient macroinvertebrate sample sizes, sample collection efforts included various habitat types such as pools, aquatic vegetation, marginal vegetation, riffles, runs, gravel, sand, and mud rather than the exact designated water quality sampling points. We also conducted active searching and handpicking. Macroinvertebrates were stored in prewashed glass bottles and preserved with prefiltered 70% v/v ethanol.

2.3. Isolation and Identification of Mps in Benthic Macroinvertebrates

MPs in macroinvertebrates were isolated according to Claessens et al. (2013) [46]. In the laboratory, macroinvertebrate samples were separated according into taxonomic families with the aid of a field guide and then categorised into feeding guilds [47], i.e., Atyidae and Corbiculidae (filter feeders; n = 92) (Figure 1c,d), Libellulidae and Gomphidae (predators; n = 128) (Figure 1e,f), and Chironomidae (grazers; n = 156) (Figure 1f). For each site, individuals per macroinvertebrate family were counted and then pooled as a single sample to allow for extraction per family and subsequent classification into feeding guilds. A 100 mL prefiltered oxidising solution of 1:3 nitric acid and hydrogen peroxide was added to a 1000 mL glass Erlenmeyer flask and covered with foil to prevent contamination. The pooled macroinvertebrate samples were carefully added and left overnight to digest without heating. No breakdown of the foil exposed to the oxidising solution was observed over the digestion period. Solutions were further heated at 100 °C for two hours and then diluted with 500 mL prefiltered deionised water, all the while keeping the flasks covered by foil.
To separate MPs into different size classes from macroinvertebrate digestates, 300 μm, 150 μm, 100 μm, 75 μm, and 25 μm sieves were stacked in descending mesh order. Each sample was retained on each test sieve and filtered through a 0.45 μm cellulose filter with grids. A 47 mm glass vacuum filtration system was used to facilitate sample filtration. Samples were allowed to dry at room temperature in a closed glass petri dish before microscopic examination. This gave MP size ranges of 25–74 µm, 75–99 µm, 100–149 µm, and 150–299 µm (no MPs 300 > μm were found). With the aid of an EZ4 Leica microscope, MPs were identified, counted, and classified per size class at 35 × magnification. For the pooled macroinvertebrate samples, the counts were converted to particles per organism (n/organism) since we knew the number of organisms per pooled sample. Microplastic content based on sample mass was not used as the organism types differed in mass per organism and body composition (Figure 1c–f).
Fifty visible MPs from the macroinvertebrate sieves, estimated as at least greater than 100 µm, were randomly selected from the cellulose filter papers for MP polymer identification (at least 135 MPs were larger than 100 μm). Only fragments and fibres could be analysed, as the small beads would snap out between the probes or tips of the forceps. Microplastic polymer identification was performed using attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR; Agilent 630, Agilent Technologies, Santa Clara, CA, USA). Microplastics were carefully picked up from the cellulose filter using anti-static forceps and placed on the ATR-FTIR diamond crystal for the MP sample polymer spectrum. Polymer identification was performed at a broad mid-infrared region of 4000–600 cm−1 at a resolution of 4 cm−1. There were 32 background scans and 43 sample scans. Each MP spectrum observed was compared with a validated plastic polymer spectrum from the S.T. Japan Spectra database ATR-FTIR library (2025). Polymer identification was accepted at confidence scores higher than 75%.

3. Quality Control

Quality control followed previously published work [40]. Sampling equipment was rinsed with prefiltered deionised water. To minimise MP contamination, all laboratory preparation work was performed in a small room cleaned for this purpose. The air-conditioning was switched off, and a cotton laboratory coat was worn. All solutions were prepared in glassware that was washed and pre-rinsed with prefiltered deionised water. Deionised water used for sample and solution preparation was prefiltered through a 0.45 μm cellulose filter paper using a 47 mm glass vacuum filtration system. Macroinvertebrates were rinsed with prefiltered water to remove extraneous MPs. Samples were covered with aluminium foil. Glass petri dishes were covered with glass lids to minimise MP contamination. All sieves were rinsed repeatedly with prefiltered deionised water before sieving each sample. Procedural blanks were kept in open glass petri dishes to account for airborne MPs. Additionally, cellulose filters used to filter preparation solutions were also kept as procedural blanks. Microplastics were absent from all procedural blanks.

Statistical Analysis

PAleontological STatistics (PAST) Version 4.09 and Graphpad Prism Version 10 were used for data analysis (www.graphpad.com) [48]. Data were tested for normal distribution using the Shapiro–Wilk test. The p-values observed were greater than 0.05, suggesting that these data were normally distributed. Therefore, a nonparametric Kruskal–Wallis (one-way ANOVA) was used to test the differences in MP contents and proportions between macroinvertebrate feeding guilds of the Sabie and Olifants rivers. The null hypothesis was that proportions of the different MP characteristics would be similar across macroinvertebrate feeding guilds, irrespective of river origin. Differences in proportions of MP colours, morphotypes, and size classes in macroinvertebrates were statistically determined using chi-square tests of actual counts. Results with p < 0.05 were considered statistically significant.

4. Results

4.1. Overall MP Content

Three hundred and seventy-six individual macroinvertebrates were collected: Atyidae and Corbiculidae (filter feeders; n = 92) (Figure 1b,c), Libellulidae and Gomphidae (predators; n = 128) (Figure 1d,e), and Chironomidae (grazers; n = 156) (Figure 1f). Corbiculidae, Libellulidae, and Gomphidae were collected from both rivers. Atyidae and Chironomidae, however, were only found in the Sabie River (see Table 1 for sample details).
In total, we isolated 365 MPs. Macroinvertebrate MP contents were analysed according to the three feeding guilds (Table 1 and Table 2). Microplastic content collected (n = 369) from all macroinvertebrate samples combined ranged from non-detected to 8.8 n/organism (Table 2). The highest MP content (8.8 n/organism) was from filter feeders, followed by predators (8.4 n/organism), and the lowest was for grazers (0.16 n/organism) (Table 2 and Supplementary Table S1). Based on the Kruskal–Wallis test (Supplementary Table S2), there were no significant differences in the number of MPs per organism between filter feeders and grazers, nor between grazers and predators. However, there was a significant difference between predators and filter feeders (p = 0.046) (Supplementary Table S2). Microplastics were found in both families that represented filter feeders, Atyidae, and Corbiculidae (Table 2). Specifically, Corbiculidae had the highest MP content, 6.8 n/organism, and 2.0 n/organism for Atyidae (Supplementary Figure S1 and Table S2). Libellulidae and Gomphidae are predatorial macroinvertebrates. Libellulidae had higher MP contents than Gomphidae (Supplementary Figure S1 and Table S2). Chironomidae, categorised as grazers, had the least MP content (0.16 n/organism) when compared with filter feeders and predators (Table 2). Again, care must be taken to interpret content values, as it is the number of MP per organism (n/organism) and not mass basis.

4.2. Microplastic Colour, Morphotype, and Size Class Proportions Between Rivers and Guilds

Do the proportional compositions of MP colours, morphotypes, and size classes in macroinvertebrates differ between rivers? And, do the proportional compositions of MP colours, morphotypes, and size classes in macroinvertebrates differ between the predatorial guild (which had the highest n/organism) when compared with all other macroinvertebrates combined from each river? This will firstly indicate differences in composition between rivers, and secondly, help determine if predatorial macroinvertebrates can be used as a proxy of MP composition of the other macroinvertebrate guilds from each river and between the two rivers.
Morphotypes: Three MP morphotypes (fibres, fragments, and microbeads; Figure 2a–c,e and Figure 3e–h) were classified. Beads were detected at higher proportions compared with fragments and fibres in all macroinvertebrates (Figure 3c,f–h). However, there was a convergence of proportions in MP morphotypes in all macroinvertebrates between the Olifants and Sabie rivers (Figure 3e). The proportional composition of morphotypes for predatorial macroinvertebrates differed significantly between the two rivers (Figure 3f). There was a significant difference in MP morphotype distribution in macroinvertebrates from both the Olifants and Sabie rivers (Figure 3g,h). A low proportion of fibres was observed in predatory macroinvertebrates from the Olifants River (Figure 3f,g), in contrast to a higher proportion observed in all macroinvertebrates from the Sabie River (Figure 3f,h). An almost equal proportion of fibres was observed in all macroinvertebrates and predators from the Olifants River (Figure 3g).
Colours: There were five different MP colours classified, i.e., red, yellow/brown, blue, black, and white (Figure 3a–d). White MPs were generally detected at higher proportions than other colours, and black the least. For all macroinvertebrates and predators, the proportions of the colours differed significantly between rivers (Figure 3a,b). In the Sabie and Olifants rivers separately, the colour proportions between all macroinvertebrates and predators also differed significantly (Figure 3c,d).
Size classes: There were four MP size classes (25–74 µm, 75–99 µm, 100–149 µm, and 150–299 µm) counted in the freshwater macroinvertebrates sampled (Figure 3i–l). No MPs larger than 300 µm were found on the 300 μm sieve. MP size class 25–75 µm was detected in a higher proportion than the other size classes (Figure 3i–l). MP size class distribution for all macroinvertebrates (Figure 3i) and predatorial macroinvertebrates (Figure 3j) differed significantly between the Olifants and Sabie rivers. The chi-square test further reflected respective significant differences when comparing all macroinvertebrates and predators from the Olifants River (p = 0.0332) and the Sabie River (p < 0.0001) (Figure 3k,l).

4.3. MP Polymer Types

Only fibres and fragments from macroinvertebrates could be characterised by ATR-FTIR (Figure 2b,e,f). Beads could not be processed as they did not stay in place between the probes. All 50 items were synthetic polymers. Five major polymer types were identified: butyl (BTL), chlorobutyl (CIIR), polyethylene (PE), polyethylene terephthalate (PET), and polypropylene (PP) (Figure 3m,n). Specifically, for macroinvertebrates, the most common polymers were BTL (34%), CIIR (20%), and PET (14%). The least common polymers collectively contributed 34% (Figure 3m). From previous data collected from the same sites at the same time [40], we have the polymer compositions of MPs in sediment. The most common polymer types for sediment were PET (39%) and PP (15%). Polyethylene, CIIR, and BTL contributed less than 15% in macroinvertebrates, respectively, and other polymers collectively contributed 22%. Comparing rubber (R) and non-rubber (NR) polymer proportions between macroinvertebrates and sediment, rubber-type polymers contributed 54% in macroinvertebrates compared with 11% in sediment (Figure 3n). Non-rubber plastic polymers contributed 89% of the sediment compared with 46% observed in macroinvertebrates (Figure 3n). The chi-square results for proportional compositions of all polymers (Figure 3m) and for rubber vs. non-rubber (Figure 3n) were significant.

5. Discussion

5.1. Microplastic Colour, Morphotype, and Size Class Proportions Between Rivers and Their Guilds

Microplastics have been characterised globally in many aquatic organisms, including macroinvertebrates [30,49,50]. The present study reports MP contents in macroinvertebrates based on colour, morphotype, and size classes in macroinvertebrate feeding guilds along two rivers with independent catchments.
The proportional MP content composition of colours, morphotypes, and size classes for all macroinvertebrates (Figure 3a,i), and for predatorial macroinvertebrates (Figure 3b,f,j) between the Olifants and Sabie rivers differed significantly, with one exception (discussed below). The same was found when all macroinvertebrates were compared with predators from the Olifants (Figure 3c,g,k) and Sabie (Figure 3d,h,l) rivers, respectively. These findings align with a study conducted in the Vipacco/Vipava River in Italy [51], which showed a significant difference between freshwater macroinvertebrate feeding guilds.
Five MP colour categories (red, yellow/brown, blue, black, and white) were found in macroinvertebrates (Figure 3a). However, yellow/brown MPs were absent from Olifants River macroinvertebrates (Figure 3a,b). The difference in MP colour profiles in macroinvertebrates between rivers (chi-square; Figure 3a) suggests that MP pollution sources differ to such an extent that they are reflected in their respective MP colour profiles. A study conducted in the Braamfontein Spruit, South Africa, suggested that the difference in macroinvertebrate MP profiles could be driven by stream characteristics such as obstructions (weirs), stream depth, and stream velocity [52]. The Olifants and Sabie rivers also have weirs, impoundments, varying river depths, and stream velocities [41,42,53].
Microplastic size class proportions also differed significantly (Figure 3i,k,l). The smallest MP size class (25–75 µm) was detected at a higher proportion than the other size classes (Figure 3i,j), whilst MPs greater than 300 µm were absent. Hence, MP size class proportions for predators also differed significantly between the Olifants and Sabie rivers (Figure 3k). This finding suggests that predatorial macroinvertebrates cannot be used as a proxy indicator of MP characteristics for other macroinvertebrates.
The significant differences observed in proportional MP content (Figure 3a–d,f–l) could be attributed to various aspects related to river-related differences in MP abundance and distribution. These aspects are not limited to local and catchment-wide differences in land use activities. Aspects such as stormwater, river characteristics, and MP physiochemical properties could affect MP abundance and distribution [3,54,55,56].
However, an important finding of the present study was the convergence of proportions in morphotypes in all macroinvertebrates between the rivers (Figure 3e). Microplastic morphotypes for all macroinvertebrates were the only characteristic variable that did not show a significant difference. This means that irrespective of MP characteristic profiles of the rivers, the macroinvertebrates retained the same morphotype proportions, suggesting that interactions with morphotypes are biologically mediated and do not reflect ambient MP characteristics. To the best of our knowledge, this study is the first to show the similarity in macroinvertebrate MP morphotype proportions between adjacent but independent rivers, despite all other MP characteristics (size, morphotype, and colour) being different.

5.2. Overall MP Contents

In the present study, we found MPs in three macroinvertebrate feeding guilds (filter feeders, predators, and grazers) (Table 1 and Table 2). Filter feeders and predators contained over fifty times the MP content (n/organism) compared with grazers (Table 2). However, there was no significant difference between the feeding guilds, except between filter feeders and predators (Supplementary Table S2). Previous studies have found that collector–gatherers (filter feeders) have significantly higher MP content compared with predatorial macroinvertebrates [51]. The significant difference in MP content between the feeding guilds can be attributed to their feeding strategies [35]. Other studies also suggested that MP uptake by some freshwater macroinvertebrates (freshwater shrimp) could be partly dependent on MP density [57].
Filter feeders: Filter feeders collect food by filtering particles in their habitat [58]. Their feeding strategy often does not discriminate between food particles and MPs [59,60]. Corbiculidae (freshwater bivalves) and Atyidae (freshwater shrimp) represented filter feeders in the current study (Table 1). Freshwater bivalves and freshwater shrimps filter settled and suspended material in their habitat [61]. This implies that MPs that settled on rocks along shorelines and water suspended MP content are bioavailable for filter feeding macroinvertebrates. Freshwater bivalves generally attach themselves to rocks along shorelines and rapids [61]. Their habitat enables them to access deposited and suspended MP content. Notably, the highest MP content for all macroinvertebrates was beads in size class 25–74 µm, followed by fibres in size class 150–299 µm (Figure 3e,i). These results reflect the findings of a previous study that recorded a high content of beads and fibres in the same size range in sediment and river water [40].
Grazers: All chironomids are considered grazers in the present study (Table 1). However, chironomids also have additional functional feeding types, namely, filter feeders, shredders, and collectors [62,63]. The chironomid MP content was the lowest when compared with the other macroinvertebrate families. Only the smallest MP size class (25–74 µm) was found in chironomids (Table 2). Microplastics of the size class 32–63 µm were mainly found in Chironomus riparius gut under laboratory conditions [64]. A study conducted in Nigeria along the Ogun and Osun rivers recorded 292 ± 27 n/g in Chironomus spp. [31]. Other studies conducted in South Africa have also observed a high MP content from Chironomidae. For instance, the MP content of about 0.0014 n/g in summer and 0.00504 n/g in winter was found in Chironomus spp. from the Bloukrans River, Grahamstown [49]. Another study conducted in the Braamfontein Spruit, Johannesburg, recorded MP concentrations ranging from 20 to 97 n/g in Chironomus spp. [13]. The high MP content found in filter feeders (Corbiculidae family) and predators of the present study is likely driven by their preferred habitat and feeding strategies [64,65]. Additionally, the presence of MPs in both Libellulidae and Gomphidae suggests that there is a potential trophic transfer of MPs from prey to predator in both the Olifants and Sabie rivers.
Predators: Libellulidae and Gomphidae we classified as predators (Table 1). Predatory macroinvertebrates generally prey on smaller prey that may include filter feeders and grazers [65], such as Chironomidae [63,66,67,68]. As a result, MPs in the gut and/or incorporated in the bodies of filter feeders and grazers are likely ingested by their predators and could accumulate [7]. However, in the current study, predatorial macroinvertebrates had the second highest MP content (Table 2). Our observation differed from a study conducted in Nigeria, where predatorial macroinvertebrates had the lowest MP contents [31]. Against expectations, Kruskal–Wallis tests (Supplementary Table S2) reflected a significant difference between predators and filter feeders (p = 0.0460). Macroinvertebrate families, such as Corbiculidae and Chironomidae, have been suggested as good bioindicators of MP pollution [31,32]. Our findings, therefore, do not support the use of the MP contents of predatorial macroinvertebrates as a proxy for MP contents for co-occurring aquatic macroinvertebrates.

5.3. Evidence of Trophic Transfer

Within predatory macroinvertebrates, the highest MP morphotypes were beads within the 25–74 µm size class, followed by fragments within the 101–150 µm size class (Table 2). The absence of MPs greater than 75 µm in Chironomidae, as opposed to the presence of MPs greater than 75 µm in predators, suggests that there is MP uptake from macroinvertebrate prey other than Chironomidae, additional uptake from the environment, or both. The macroinvertebrate families we studied might not have direct trophic links in the river ecosystems we studied. However, although we found little evidence of trophic transfer between the feeding guilds we studied, MPs in or on the macroinvertebrates may be transferred to other higher trophic-level aquatic (such as fish) and terrestrial animals (such as egrets and kingfishers) that consume aquatic macroinvertebrates [68].

5.4. MP Polymer Types

We determined MP polymer types to deduce possible MP sources based on their polymer compositions. Amongst the five different types of polymers found, two polymers (butyl and chlorobutyl) dominated (Figure 3m,n). Both butyl (BTL) and chlorobutyl (CIIR) are natural rubber co-polymers commonly used in vehicle tyre manufacturing [69]. Approximately 0.2–5.5 kg per capita per year of tyre thread is estimated to be released into the natural environment [70]. Hence, a high proportion (94%) of synthetic rubber was recorded in Tema Navo marine sediment [71]. Based on a model, approximately 42% of MPs in the sea result from tyre and road wear particles that are transported there by rivers [72]. KNP uses road transport for tourism, conservation, and logistics, and it is a likely source within KNP in addition to what is carried in from upstream, translating to 34% and 20% of BTL and CIIR polymer ingestion by macroinvertebrates, respectively. These particles could also originate from conveyor belts [73] used in mining in the upper catchments, especially on the Olifants River.
Diatoms and macroinvertebrates colonise plastic polymers [27]. The epibiont biofilms that develop on the surface of plastics [74] may stimulate the ingestion of MPs by invertebrates, as they may taste similar to their prey [13]. In addition, plastics in freshwaters emit dimethyl sulphide (which is a foraging cue) due to the action of non-photosynthetic biofilm components [75]. Against expectation, rubber polymer (BTL and CIIR) proportions were approximately five times higher in macroinvertebrates than in sediment (Figure 3n). Rubber polymers serve as an artificial substrate used to cultivate diatoms because they support higher diatom abundance than natural substrates, such as rocks [76]. As a result, macroinvertebrates might ingest rubber polymer MPs more than MPs of other polymers while grazing on diatoms. This may explain the preponderance of rubber-type polymers in the macroinvertebrates (Figure 3n), but this needs much more research. Although some MP polymers contributed the least (Figure 3m), their presence could still pose threats [23,49,77].

6. Conclusions and Recommendations

We investigated the proportional compositions of MP colours, morphotypes, and size classes in macroinvertebrates between two rivers. The advantage of this study was that we had two independent rivers, allowing independent ‘duplicate’ tests of various questions. We, therefore, determined if proportional compositions of MP colours, morphotypes, and size classes in macroinvertebrates differ between the predators and all other macroinvertebrates combined, from and between each river. Our results show that macroinvertebrates from the two rivers had MPs in or on them—some probably in the digestive tract from ingestion and others incorporated in tissues [30,36,64].
A previous study recorded higher MP concentration in the water and sediment from the Olifants compared with the Sabie River [40]. Unexpectedly, however, macroinvertebrates from the less polluted Sabie River had higher MP content compared with macroinvertebrates from the more polluted Olifants River. This may be because the water and sediment samples were collected four months after the macroinvertebrates were collected, suggesting that macroinvertebrate loadings reflect short-term ambient variations, an aspect that would need more attention.
Although MPs were detected in all sampled feeding guilds, macroinvertebrates seemed to interact with MPs at different contents, morphotypes, sizes, and colours. Based on MP colour, size, and morphotypes, there were significant differences in proportional compositions between the predatorial macroinvertebrates and the other macroinvertebrates. Predatorial macroinvertebrates, therefore, cannot be used as an indicator of MP characteristics for other macroinvertebrates. However, there was a convergence of proportions in MP morphotypes in all macroinvertebrates between the rivers. This implies that the macroinvertebrates overall retained the same morphotype proportions, irrespective of the differing MP characteristic profiles of the rivers, suggesting that interactions with morphotypes are biologically mediated and do not reflect ambient MP characteristics.
The presence of MPs in macroinvertebrates highlights the importance of implementing policies banning microbeads in personal care products and eliminating single-use plastics in South Africa and its protected areas. The dominant polymer types were BTL and CIIR, which are natural rubber co-polymers commonly used in vehicle tyre and conveyor belt manufacturing. Thus, the impact of tyre wear and conveyor belt residues on macroinvertebrates is of great importance for further investigations. It is important to reduce MP emissions, monitor their presence and dynamics in freshwaters, and research possible effects. Finally, although we found little evidence of trophic transfer between the feeding guilds we studied, aquatic macroinvertebrates may be vectors of MPs to eventually higher trophic aquatic and terrestrial levels, such as crocodiles, tigerfish, egrets, and fish eagles, especially in protected areas, such as KNP.

7. Study Limitations

Since not all equivalent macroinvertebrate taxa were available at each site and from each river, feeding guilds were used for comparisons. External contamination during sampling seems unlikely to have an effect given the large differences in MP morphotypes, sizes, colours, and polymer type between feeding guilds, sites, and rivers, andwhen compared with previously published sediment results, the samples for both were collected at the same time [40]. A single plastic product could be manufactured using different plastic polymer types [4]. Also, different plastic products eventually share the same water body, resulting in plastic polymer source correlation difficulties. We did not check for MP recovery, except for when relying on sieve mesh retention after digestion. Microplastic size selection for ATR was limited by what could be manually picked up from the sieves, 50 out of 365, which is more than proposed by Cowger et al. (2024) [78], albeit biased towards larger MPs. Otherwise, except for digestions, procedures used were the same as those by Shikwambana et al. (2024) [40], facilitating comparability.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/w17111579/s1, Table S1: Microplastic particle content extracted from different freshwater benthic macroinvertebrate feeding guild pools from the Sabie and Olifants rivers. Table S2: Kruskal–Wallis test for equal medians. Figure S1: Microplastic particle counts from macroinvertebrates along the Olifants and Sabie rivers.

Author Contributions

Conceptualisation, P.S., L.C.F., H.B., J.B. and J.C.T.; methodology, P.S., L.C.F., H.B., J.B. and J.C.T.; software, H.B.; formal analysis, P.S., L.C.F., H.B. and J.B.; investigation, P.S.; data curation, P.S., L.C.F., H.B. and J.B.; writing—original draft preparation, P.S., L.C.F., H.B., J.B. and J.C.T.; writing—review and editing, P.S., L.C.F., H.B., J.B. and J.C.T.; supervision, L.C.F., H.B. and J.C.T.; funding acquisition, J.C.T. All authors have read and agreed to the published version of the manuscript.

Funding

The following institutions provided financial support for this project: the South African National Parks (SANParks), North-West University (NWU), and the University of Mpumalanga (UMP).

Institutional Review Board Statement

Research and sample collection permission was granted by the South African National Parks (SANParks) Scientific Service Department under research permit number SHIP1551. The North West University provided Research Ethical Clearance (NWU—01639-20-A9).

Data Availability Statement

This data cannot be shared for public access at this stage because they are required for a Risk Assessment study. SANParks is the custodian of these data, and they will be available upon request after the risk assessment study research work is published. Data requests can be directed to Gisuser@sanparks.org.

Acknowledgments

Accommodation and transportation to the field were provided by SANParks. Sampling equipment and laboratory equipment, such as FTIR, were provided by NWU. Finally, UMP provided the support required for sample analysis and data analysis. We are grateful to the following individuals: Velly Ndlovu, for being our game guard throughout the MP sampling season, Sipokazi Bam, for assisting with the KNP MAP, and Willie Landman, for ATR-FTIR training and polymer identification techniques.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Aragaw, T.A. Microplastic pollution in African countries’ water systems: A review on findings, applied methods, characteristics, impacts, and managements. SN Appl. Sci. 2021, 3, 629. [Google Scholar] [CrossRef] [PubMed]
  2. Yan, M.; Wang, L.; Dai, Y.; Sun, H.; Liu, C. Behavior of Microplastics in Inland Waters: Aggregation, Settlement, and Transport. Bull. Environ. Contam. Toxicol. 2021, 107, 700–709. [Google Scholar] [CrossRef]
  3. Saad, D. Why Microplastics Are Exceptional Contaminants? 2023. Available online: https://www.intechopen.com/ (accessed on 4 May 2024).
  4. Geyer, R.; Jambeck, J.R.; Law, K.L. Production, use, and fate of all plastics ever made [Producción, uso y destino de todos los plásticos jamás fabricados]. Sci. Adv. 2017, 3, e1700782. [Google Scholar] [CrossRef]
  5. Wagner, M.; Lambert, S. Freshwater Microplastics The Handbook of Environmental Chemistry 58 Series; Barceló, D., Kostianoy, A.G., Eds.; Springer: Cham, Switzerland, 2018. [Google Scholar]
  6. Horton, A.A.; Svendsen, C.; Williams, R.J.; Spurgeon, D.J.; Lahive, E. Large microplastic particles in sediments of tributaries of the River Thames, UK—Abundance, sources and methods for effective quantification. Mar. Pollut. Bull. 2017, 114, 218–226. [Google Scholar] [CrossRef]
  7. Mason, S.A.; Garneau, D.; Sutton, R.; Chu, Y.; Ehmann, K.; Barnes, J.; Fink, P.; Papazissimos, D.; Rogers, D.L. Microplastic pollution is widely detected in US municipal wastewater treatment plant effluent. Environ. Pollut. 2016, 218, 1045–1054. [Google Scholar] [CrossRef]
  8. Covernton, G.A.; Cox, K. Commentary on: Abundance and distribution of microplastics within surface sediments of a key shellfish growing region of Canada. PLoS ONE 2019, 14, e0225945. [Google Scholar] [CrossRef]
  9. Hernandez, E.; Nowack, B.; Mitrano, D.M. Polyester Textiles as a Source of Microplastics from Households: A Mechanistic Study to Understand Microfiber Release during Washing. Environ. Sci. Technol. 2017, 51, 7036–7046. [Google Scholar] [CrossRef]
  10. Verster, C.; Bouwman, H. Land-based sources and pathways of marine plastics in a South African context. S. Afr. J. Sci. 2020, 116, 1–9. [Google Scholar] [CrossRef]
  11. Maleka, T.; Greenfield, R.; Muniyasamy, S.; Modley, L.A. An overview on the characterization of microplastics (MPs) in waste water treatment plants (WWTPs). Sustain. Water Resour. Manag. 2024, 10, 182. [Google Scholar] [CrossRef]
  12. Tibbetts, J.; Krause, S.; Lynch, I.; Smith, G.H.S. Abundance, distribution, and drivers of microplastic contamination in urban river environments. Water 2018, 10, 1597. [Google Scholar] [CrossRef]
  13. Dahms, H.T.J.; van Rensburg, G.J.; Greenfield, R. The microplastic profile of an urban African stream. Sci. Total Environ. 2020, 731, 138893. [Google Scholar] [CrossRef] [PubMed]
  14. Yakubu, S.; Miao, B.; Hou, M.; Zhao, Y. A review of the ecotoxicological status of microplastic pollution in African freshwater systems. Sci. Total Environ. 2024, 946, 174092. [Google Scholar] [CrossRef] [PubMed]
  15. Silva, A.B.; Costa, M.F.; Duarte, A.C. Biotechnology advances for dealing with environmental pollution by micro(nano)plastics: Lessons on theory and practices. Curr. Opin. Environ. Sci. Health 2018, 1, 30–35. [Google Scholar] [CrossRef]
  16. Chang, M. Reducing microplastics from facial exfoliating cleansers in wastewater through treatment versus consumer product decisions. Mar. Pollut. Bull. 2015, 101, 330–333. [Google Scholar] [CrossRef]
  17. Clapp, J.; Swanston, L. Doing away with plastic shopping bags: International patterns of norm emergence and policy implementation. Environ. Politics 2009, 18, 315–332. [Google Scholar] [CrossRef]
  18. Xanthos, D.; Walker, T.R. International policies to reduce plastic marine pollution from single-use plastics (plastic bags and microbeads): A review. Mar. Pollut. Bull. 2017, 118, 17–26. [Google Scholar] [CrossRef]
  19. Royer, S.; Greco, F.; Kogler, M.; Deheyn, D.D. Not so biodegradable: Polylactic acid and cellulose/plastic blend textiles lack fast biodegradation in marine waters. PLoS ONE 2023, 18, e0284681. [Google Scholar] [CrossRef]
  20. Leblanc, R. How Long Garbage Decomposes. 2015. Available online: https://www.richlandcenterwi.gov/sites/default/files/fileattachments/parks_amp_recreation/page/2534/howlonggarbagedecomposes.pdf (accessed on 5 May 2024).
  21. Saad, D.; Alamin, H. The first evidence of microplastic presence in the River Nile in Khartoum, Sudan: Using Nile tilapia fish as a bio-indicator. Heliyon 2024, 10, e23393. [Google Scholar] [CrossRef]
  22. Ma, Y.; You, X. Microplastics in freshwater ecosystems: A significant force of disrupting health and altering trophic transfer patterns by reduced assimilation efficiency of aquatic organisms. Aquaculture 2025, 594, 741463. [Google Scholar] [CrossRef]
  23. Emon, F.J.; Hasan, J.; Shahriar, S.I.M.; Islam, N.; Islam, M.S.; Shahjahan, M. Increased ingestion and toxicity of polyamide microplastics in Nile tilapia with increase of salinity. Ecotoxicol. Environ. Saf. 2024, 282, 116730. [Google Scholar] [CrossRef]
  24. Devriese, L.I.; De Witte, B.; Vethaak, A.D.; Hostens, K.; Leslie, H.A. Bioaccumulation of PCBs from microplastics in Norway lobster (Nephrops norvegicus): An experimental study. Chemosphere 2017, 186, 10–16. [Google Scholar] [CrossRef] [PubMed]
  25. Nava, V.; Matias, M.G.; Castillo-Escrivà, A.; Messyasz, B.; Leoni, B. Microalgae colonization of different microplastic polymers in experimental mesocosms across an environmental gradient. Glob. Change Biol. 2022, 28, 1402–1413. [Google Scholar] [CrossRef] [PubMed]
  26. Taurozzi, D.; Cesarini, G.; Scalici, M. Diatom and macroinvertebrate communities dynamic: A co-occurrence pattern analysis on plastic substrates. Sci. Total Environ. 2024, 912, 169071. [Google Scholar] [CrossRef] [PubMed]
  27. Taurozzi, D.; Cesarini, G.; Scalici, M. New ecological frontiers in the plastisphere: Diatoms and macroinvertebrates turnover assessment by a traits-based approach. Sci. Total Environ. 2023, 887, 164186. [Google Scholar] [CrossRef]
  28. Sun, L.; Cheng, Z.; Wang, M.; Wei, C.; Liu, H.; Yang, Y. A multi-levels analysis to evaluate the toxicity of microplastics on aquatic insects: A case study with damselfly larvae (Ischnura elegans). Ecotoxicol. Environ. Saf. 2025, 289, 117447. [Google Scholar] [CrossRef]
  29. Sbarberi, R.; Magni, S.; Ponti, B.; Tediosi, E.; Neri, M.C.; Binelli, A. Multigenerational effects of virgin and sampled plastics on the benthic macroinvertebrate Chironomus riparius. Aquat. Toxicol. 2025, 279, 107205. [Google Scholar] [CrossRef]
  30. Ghosh, T. Microplastics bioaccumulation in fish: Its potential toxic effects on hematology, immune response, neurotoxicity, oxidative stress, growth, and reproductive dysfunction. Toxicol. Rep. 2025, 14, 101854. [Google Scholar] [CrossRef]
  31. Akindele, E.O.; Ehlers, S.M.; Koop, J.H.E. Freshwater insects of different feeding guilds ingest microplastics in two Gulf of Guinea tributaries in Nigeria. Environ. Sci. Pollut. Res. 2020, 27, 33373–33379. [Google Scholar] [CrossRef]
  32. Parra, S.; Varandas, S.; Santos, D.; Félix, L.; Fernandes, L.; Cabecinha, E.; Gago, J.; Monteiro, S.M. Multi-biomarker responses of Asian clam Corbicula fluminea (Bivalvia, Corbiculidea) to cadmium and microplastics pollutants. Water 2021, 13, 394. [Google Scholar] [CrossRef]
  33. Dickens, C.W.S.; Graham, P.M.; Dickens, C.W.S.; Graham, P.M. The South African Scoring System (SASS) Version 5 Rapid Bioassessment Method for Rivers The South African Scoring System (SASS) Version 5 Rapid Bioassessment. Afr. J. Aquat. Sci. 2010, 27, 1–10. [Google Scholar] [CrossRef]
  34. Mangadze, T.; Bere, T.; Mwedzi, T. Choice of biota in stream assessment and monitoring programs in tropical streams: A comparison of diatoms, macroinvertebrates and fish. Ecol. Indic. 2016, 63, 128–143. [Google Scholar] [CrossRef]
  35. Porter, A.; Godbold, J.A.; Lewis, C.N.; Savage, G.; Solan, M.; Galloway, T.S. Microplastic burden in marine benthic invertebrates depends on species traits and feeding ecology within biogeographical provinces. Nat. Commun. 2023, 14, 8023. [Google Scholar] [CrossRef] [PubMed]
  36. Benhadji, N.; Kurniawan, S.B.; Imron, M.F. Review of mayflies (Insecta Ephemeroptera) as a bioindicator of heavy metals and microplastics in freshwater. Sci. Total Environ. 2025, 958, 178057. [Google Scholar] [CrossRef] [PubMed]
  37. Huang, W.; Song, S.; Liang, J.; Niu, Q.; Zeng, G.; Shen, M.; Deng, J.; Luo, Y.; Wen, X.; Zhang, Y. Microplastics and associated contaminants in the aquatic environment: A review on their ecotoxicological effects, trophic transfer, and potential impacts to human health. J. Hazard. Mater. 2021, 405, 124187. [Google Scholar] [CrossRef]
  38. Mbedzi, R.; Cuthbert, R.N.; Wasserman, R.J.; Murungweni, F.M.; Dalu, T. Spatiotemporal variation in microplastic contamination along a subtropical reservoir shoreline. Environ. Sci. Pollut. Res. 2020, 27, 23880–23887. [Google Scholar] [CrossRef]
  39. Riddell, E.S.; Govender, D.; Botha, J.; Sithole, H.; Petersen, R.M.; Shikwambana, P. Pollution impacts on the aquatic ecosystems of the Kruger National Park, South Africa. Sci. Afr. 2019, 6, e00195. [Google Scholar] [CrossRef]
  40. Shikwambana, P.; Foxcroft, L.C.; Taylor, J.C.; Bouwman, H. Microplastic Concentrations in Sediments and Waters Do Not Decrease in Two Rivers Flowing Through the Kruger National Park, South Africa. Water Air Soil Pollut. 2024, 235, 675. [Google Scholar] [CrossRef]
  41. Pollard, S.; Laporte, A. Overview of the Olifants Catchment. No. March. 2014. Available online: http://award.org.za/wp/wp-content/uploads/2021/04/AWARD-TECH-REPORT-53-Overview-of-the-Olifants-Catchment-March-2014-v1.pdf (accessed on 5 May 2024).
  42. Moolman, J.; King, J.; Thirion, C. Channel Slopes in the Olifants, Crocodile and Sabie River Catchments. 2002; pp. 1–42. Available online: https://award.org.za/wp/wp-content/uploads/2020/07/AWARD-TECH-REPORT-40-Overview-of-the-Olifants-catchment-2014-v1.pdf (accessed on 4 May 2024).
  43. Pollard, E.S. Testing Strategic Adaptive Management during Crisis: Management of the Perennial Rivers of the Kruger National Park during Drought. In Proceedings of the 14th International Water Association (IWA) Specialist Conference on Watershed and River Basin Management, Skukuza, South Africa, 9–11 October 2017. [Google Scholar]
  44. Biggs, H.C.; Clifford-Holmes, J.K.; Freitag, S.; Venter, F.J.; Venter, J. Cross-scale governance and ecosystem service delivery: A case narrative from the Olifants River in north-eastern South Africa. Ecosyst. Serv. 2017, 28, 173–184. [Google Scholar] [CrossRef]
  45. Statistics South Africa. Midyear Population Estimate 2019; Statistics South Africa: Cape Town, South Africa, 2019; p. 24. [Google Scholar]
  46. Claessens, M.; Van Cauwenberghe, L.; Vandegehuchte, M.B.; Janssen, C.R. New techniques for the detection of microplastics in sediments and field collected organisms. Mar. Pollut. Bull. 2013, 70, 227–233. [Google Scholar] [CrossRef]
  47. Gerber, A.; Gabriel, M.J.M. Aquatic Invertebrates of South African Rivers Field Guide; Department of Water Affairs and Forestry: Pretoria, South Africa, 2002. [Google Scholar]
  48. Hammer, Ø.; Harper, D.A.T.; Ryan, P.D. Past Palaeontological Statistics, Ver. 1.79. 2001; pp. 1–88. Available online: https://palaeo-electronica.org/2001_1/past/past.pdf (accessed on 20 January 2023).
  49. Nel, H.A.; Dalu, T.; Wasserman, R.J. Sinks and sources: Assessing microplastic abundance in river sediment and deposit feeders in an Austral temperate urban river system. Sci. Total Environ. 2018, 612, 950–956. [Google Scholar] [CrossRef]
  50. Eerkes-Medrano, D.; Thompson, R.C.; Aldridge, D.C. Microplastics in freshwater systems: A review of the emerging threats, identification of knowledge gaps and prioritisation of research needs. Water Res. 2015, 75, 63–82. [Google Scholar] [CrossRef] [PubMed]
  51. Bertoli, M.; Pastorino, P.; Lesa, D.; Renzi, M.; Anselmi, S.; Prearo, M.; Pizzul, E. Microplastics accumulation in functional feeding guilds and functional habit groups of freshwater macrobenthic invertebrates: Novel insights in a riverine ecosystem. Sci. Total Environ. 2022, 804, 150207. [Google Scholar] [CrossRef]
  52. Dahms, H.T.J.; Tweddle, G.P.; Greenfield, R. Gastric Microplastics in Clarias gariepinus of the Upper Vaal River, South Africa. Front. Environ. Sci. 2022, 10, 931073. [Google Scholar] [CrossRef]
  53. Weeks, D.C.; O’Keeffe, J.H.; Fourie, A.; Davies, B.R. A Pre-Impoundment Study of the Sabie-Sand River System, Mpumalanga With Special Reference To Predicted Impacts on the Kruger National Park. Water Res. Comm. 1996, 294, 96. [Google Scholar]
  54. Monira, S.; Bhuiyan, M.; Haque, N.; Shah, K.; Roychand, R.; Hai, F.I.; Premanik, B.K. Understanding the fate and control of road dust-associated microplastics in stormwater. Process Saf. Environ. Prot. 2021, 152, 47–57. [Google Scholar] [CrossRef]
  55. Peller, J.R.; Tabor, G.; Davis, C.; Iceman, C.; Nwachukwu, O.; Doudrick, K.; Wilson, A.; Suprenant, A.; Dabertin, D.; McCool, J.-P. Distribution and Fate of Polyethylene Microplastics Released by a Portable Toilet Manufacturer into a Freshwater Wetland and Lake. Water 2024, 16, 11. [Google Scholar] [CrossRef]
  56. Duis, K.; Coors, A. Microplastics in the aquatic and terrestrial environment: Sources (with a specific focus on personal care products), fate and effects. Environ. Sci. Eur. 2016, 28, 2. [Google Scholar] [CrossRef]
  57. Dahms, H.T.J.; Greenfield, R.; Dalu, T.; Themba, N.N.; Dondofema, F.; Cuthbert, R.N. Nowhere to go! Microplastic abundances in freshwater fishes living near wastewater plants. Environ. Toxicol. Pharmacol. 2023, 101, 104210. [Google Scholar] [CrossRef]
  58. Szałkiewicz, E.; Kałuża, T.; Grygoruk, M. Detailed analysis of habitat suitability curves for macroinvertebrates and functional feeding groups. Sci. Rep. 2022, 12, 10757. [Google Scholar] [CrossRef]
  59. Goss, H.; Jaskiel, J.; Rotjan, R. Thalassia testudinum as a potential vector for incorporating microplastics into benthic marine food webs. Mar. Pollut. Bull. 2018, 135, 1085–1089. [Google Scholar] [CrossRef]
  60. Guo, F.; Bunn, S.E.; Brett, M.T.; Fry, B.; Hager, H.; Ouyang, X.; Kainz, M.J. Feeding strategies for the acquisition of high-quality food sources in stream macroinvertebrates: Collecting, integrating, and mixed feeding. Limnol. Oceanogr. 2018, 63, 1964–1978. [Google Scholar] [CrossRef] [PubMed]
  61. Vaughn, C.C.; Hoellein, T.J. Bivalve impacts in freshwater and marine ecosystems. Annu. Rev. Ecol. Evol. Syst. 2018, 49, 183–208. [Google Scholar] [CrossRef]
  62. Antczak-Orlewska, O.; Płóciennik, M.; Sobczyk, R.; Okupny, D.; Stachowicz-Rybka, R.; Rzodkiewicz, M.; Siciński, J.; Mroczkowska, A.; Krąpiec, M.; Słowiński, M.; et al. Chironomidae Morphological Types and Functional Feeding Groups as a Habitat Complexity Vestige. Front. Ecol. Evol. 2021, 8, 583831. [Google Scholar] [CrossRef]
  63. Makgoale, M.M.; Addo-Bediako, A.; Ayisi, K.K. Distribution Pattern of Macroinvertebrate Functional Feeding Groups in the Steelpoort River, South Africa. Appl. Ecol. Environ. Res. 2022, 20, 189–206. [Google Scholar] [CrossRef]
  64. Scherer, C.; Brennholt, N.; Reifferscheid, G.; Wagner, M. Feeding type and development drive the ingestion of microplastics by freshwater invertebrates. Sci. Rep. 2017, 7, 17006. [Google Scholar] [CrossRef]
  65. Uwadiae, R.E. Macroinvertebrates functional feeding groups as indices of biological assessment in a tropical aquatic ecosystem: Implications for ecosystem functions. N. Y. Sci. J. 2010, 3, 6–15. [Google Scholar]
  66. Nhiwatiwa, T.; Brendonck, L.; Dalu, T. Understanding factors structuring zooplankton and macroinvertebrate assemblages in ephemeral pans. Limnologica 2017, 64, 11–19. [Google Scholar] [CrossRef]
  67. Addo-Bediako, A. Spatial distribution patterns of benthic macroinvertebrate functional feeding groups in two rivers of the olifants river system, South Africa. J. Freshw. Ecol. 2021, 36, 97–109. [Google Scholar] [CrossRef]
  68. Lourenço, P.M.; Serra-Gonçalves, C.; Ferreira, J.L.; Catry, T.; Granadeiro, J.P. Plastic and other microfibers in sediments, macroinvertebrates and shorebirds from three intertidal wetlands of southern Europe and west Africa. Environ. Pollut. 2017, 231, 123–133. [Google Scholar] [CrossRef]
  69. Paduvilan, J.K.; Velayudhan, P.; Amanulla, A.; Maria, H.J.; Saiter-fourcin, A.; Thomas, S. Assessment of Graphene Oxide and Nanoclay Based Hybrid Filler in Chlorobutyl-Natural Rubber Blend for Advanced Gas Barrier Applications. Nanomaterials 2021, 11, 1098. [Google Scholar] [CrossRef]
  70. Baensch-Baltruschat, B.; Kocher, B.; Stock, F.; Reifferscheid, G. Tyre and road wear particles (TRWP)—A review of generation, properties, emissions, human health risk, ecotoxicity, and fate in the environment. Sci. Total Environ. 2020, 733, 137823. [Google Scholar] [CrossRef] [PubMed]
  71. Munari, C.; Infantini, V.; Scoponi, M.; Rastelli, E.; Corinaldesi, C.; Mistri, M. Microplastics in the sediments of Terra Nova Bay (Ross Sea, Antarctica). Mar. Pollut. Bull. 2017, 122, 161–165. [Google Scholar] [CrossRef] [PubMed]
  72. Siegfried, M.; Koelmans, A.A.; Besseling, E.; Kroeze, C. Export of microplastics from land to sea. A modelling approach. Water Res. 2017, 127, 249–257. [Google Scholar] [CrossRef]
  73. Zhang, Q.; Wang, R.; Shen, Y.; Zhan, L.; Xu, Z. An ignored potential microplastic contamination of a typical waste glass recycling base. J. Hazard. Mater. 2022, 422, 126854. [Google Scholar] [CrossRef] [PubMed]
  74. Jiang, Y.; Niu, S.; Wu, J. The role of algae in regulating the fate of microplastics: A review for processes, mechanisms, and influencing factors. Sci. Total Environ. 2024, 949, 175227. [Google Scholar] [CrossRef]
  75. Valentine, K.; Hughes, C.; Boxall, A. Plastic Litter Emits the Foraging Infochemical Dimethyl Sulfide after Submersion in Freshwater Rivers. Environ. Toxicol. Chem. 2024, 47, 1485–1496. [Google Scholar] [CrossRef]
  76. Nenadović, T.; Šarčević, T.; Čižmek, H.; Godrijan, J.; Marić Pfannkuchen, D.; Pfannkuchen, M.; Ljubešić, Z. Development of periphytic diatoms on different artificial substrates in the Eastern Adriatic Sea. Acta Bot. Croat. 2015, 74, 377–392. [Google Scholar] [CrossRef]
  77. Yuan, Z.; Nag, R.; Cummins, E. Ranking of potential hazards from microplastics polymers in the marine environment. J. Hazard. Mater. 2022, 429, 128399. [Google Scholar] [CrossRef]
  78. Cowger, W.; Markley, L.A.T.; Moore, S.; Gray, A.B.; Upadhyay, K.; Koelmans, A.A. How many microplastics do you need to (sub)sample? Ecotoxicol. Environ. Saf. 2024, 275, 116243. [Google Scholar] [CrossRef]
Water 17 01579 g001
Figure 1. Macroinvertebrate sampling sites along the Olifants and Sabie rivers. (a) Images of macroinvertebrate families, (b) Atyidae, freshwater shrimp (filter feeder), (c) Corbiculidae, freshwater bivalve (filter feeder), (d) Libellulidae, dragonfly nymph (predator), (e) Gomphidae, dragonfly nymph (predator), and (f) Chironomidae, midge (grazer). (Photos by P Shikwambana and H Sithole).
Figure 1. Macroinvertebrate sampling sites along the Olifants and Sabie rivers. (a) Images of macroinvertebrate families, (b) Atyidae, freshwater shrimp (filter feeder), (c) Corbiculidae, freshwater bivalve (filter feeder), (d) Libellulidae, dragonfly nymph (predator), (e) Gomphidae, dragonfly nymph (predator), and (f) Chironomidae, midge (grazer). (Photos by P Shikwambana and H Sithole).
Water 17 01579 g001
Water 17 01579 g002
Figure 2. (a) MP fragment, (b) MP fibre, (c) MP bead, (d) diatoms, (e) MP fibre from the clam in Figure 1d, (f) ATR-FTIR spectrum of a polyester fibre.
Figure 2. (a) MP fragment, (b) MP fibre, (c) MP bead, (d) diatoms, (e) MP fibre from the clam in Figure 1d, (f) ATR-FTIR spectrum of a polyester fibre.
Water 17 01579 g002
Water 17 01579 g003
Figure 3. Bar graphs showing MP frequency according to colour, morphotype, and size classes for all sampled macroinvertebrates along the Olifants and Sabie rivers (a–l). The p-values in (a–l) reflect the outcomes of chi-square analyses for differences in proportions. Statistically significant p-values are in bold. The proportional MP polymer compositions for macroinvertebrates and sediment are reflected in (m) (all polymers) and (n) (rubber vs. non-rubber).
Figure 3. Bar graphs showing MP frequency according to colour, morphotype, and size classes for all sampled macroinvertebrates along the Olifants and Sabie rivers (a–l). The p-values in (a–l) reflect the outcomes of chi-square analyses for differences in proportions. Statistically significant p-values are in bold. The proportional MP polymer compositions for macroinvertebrates and sediment are reflected in (m) (all polymers) and (n) (rubber vs. non-rubber).
Water 17 01579 g003
Table 1. Macroinvertebrate sample number, name, feeding guild, number of organisms, site ID, and sample site GPS coordinates.
Table 1. Macroinvertebrate sample number, name, feeding guild, number of organisms, site ID, and sample site GPS coordinates.
SampleMacroinvertebrateGuildRiverNumberSite IDLatLong
O10GOMGomphidaePredatorOlifants7O631.42029°−24.3162°
O5LABLibellulidaePredatorOlifants11O231.37197°−23.9215°
O6GOMGomphidaePredatorOlifants23O631.42029°−24.0527°
O7CORCorbiculidaeFilterOlifants26O231.22318°−24.0471°
O8CORCorbiculidaeFilterOlifants24O631.42029°−24.3162°
O9LABLibellulidaePredatorOlifants17O631.42029°−24.3162°
S11CORCorbiculidaeFilterSabie17S231.29239°−24.9883°
S11ATYAtyidaeFilterSabie25S831.92460°−25.1219°
S2CHIChironomidaeGrazerSabie156S131.21729°−25.0194°
S3GOMGomphidaePredatorSabie56S231.29239°−24.9883°
S4LABLibellulidaePredatorSabie14S231.29239°−24.9883°
Table 2. Mean MP contents (n/organism) per MP size classes in macroinvertebrates per feeding guild from the Sabie and Olifants rivers combined.
Table 2. Mean MP contents (n/organism) per MP size classes in macroinvertebrates per feeding guild from the Sabie and Olifants rivers combined.
Feeding GuildMP Size Classes
25–75 µm76–100 µm101–150 µm151–299 µmTotal
Filter feeder (n = 92)3.12.20.722.88.8
FibreNDND0.162.83.0
Fragment0.711.30.56ND2.6
Bead2.40.95NDND3.3
Grazer (n = 156)0.16NDNDND0.16
Fibre0.03NDNDND0.03
Fragment0.11NDNDND0.1
Bead0.01NDNDND0.01
Predator (n = 128)4.20.082.41.88.5
Fibre0.14ND0.141.21.5
Fragment0.5ND2.20.63.3
Bead3.50.08NDND3.5
Note: ND—not detected.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Shikwambana, P.; Foxcroft, L.C.; Bouwman, H.; Botha, J.; Taylor, J.C. Contrasting Microplastic Characteristics in Macroinvertebrates from Two Independent but Adjacent Rivers in Kruger National Park, South Africa. Water 2025, 17, 1579. https://doi.org/10.3390/w17111579

AMA Style

Shikwambana P, Foxcroft LC, Bouwman H, Botha J, Taylor JC. Contrasting Microplastic Characteristics in Macroinvertebrates from Two Independent but Adjacent Rivers in Kruger National Park, South Africa. Water. 2025; 17(11):1579. https://doi.org/10.3390/w17111579

Chicago/Turabian Style

Shikwambana, Purvance, Llewellyn C. Foxcroft, Hindrik Bouwman, Judith Botha, and Jonathan C. Taylor. 2025. "Contrasting Microplastic Characteristics in Macroinvertebrates from Two Independent but Adjacent Rivers in Kruger National Park, South Africa" Water 17, no. 11: 1579. https://doi.org/10.3390/w17111579

APA Style

Shikwambana, P., Foxcroft, L. C., Bouwman, H., Botha, J., & Taylor, J. C. (2025). Contrasting Microplastic Characteristics in Macroinvertebrates from Two Independent but Adjacent Rivers in Kruger National Park, South Africa. Water, 17(11), 1579. https://doi.org/10.3390/w17111579

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop