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Article

Composting as a Sustainable Solution for the Management of Plant Biomass Contaminated with Hg and As from Puddles Generated by Small-Scale Gold Mining in the Municipality of Unión Panamericana, Colombian Pacific

by
Gysela Rengifo-Mosquera
1,
Manuel Salas-Moreno
1,
Harry Gutierréz-Palacios
2,
Yuber Palacios-Torres
3,
Allien Romaña-Palacios
3 and
José Marrugo-Negrete
4,*
1
Grupo de Investigación en Biosistemática, Departamento de Biología, Facultad de Ciencias Naturales, Universidad Tecnológica del Chocó, Carrera 22 No. 18B-10, Quibdó 270002, Chocó, Colombia
2
Facultad de Ingeniería, Universidad Tecnológica del Chocó, Carrera 22 No. 18B-10, Quibdó 270002, Chocó, Colombia
3
Grupo de Recursos Naturales y Toxicología Ambiental, Facultad de Ciencias Naturales, Universidad Tecnológica del Chocó, Chocó, A.A. 292, Quibdó 270002, Chocó, Colombia
4
Departamento de Química, Facultad de Ciencias Básicas, Grupo de Agua, Química Aplicada y Ambiental, Universidad de Córdoba, Carrera 6 No. 76-103, Montería 230003, Córdoba, Colombia
*
Author to whom correspondence should be addressed.
Sustainability 2024, 16(22), 9940; https://doi.org/10.3390/su16229940
Submission received: 19 September 2024 / Revised: 30 October 2024 / Accepted: 6 November 2024 / Published: 14 November 2024
(This article belongs to the Special Issue Sustainable Remediation of Soil and Water Contaminant: Innovations and Practices)
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Abstract

:
ASGM in the Chocó region (Colombian Pacific) has generated abandoned puddles with concentrations of Hg; however, these sites can generate ecosystem services from contaminated biomass with a circular economy approach. (1) Background: The plant biomass contaminated with Hg from these puddles could be used to produce compost as a bioremediation strategy and as an alternative to generate ecosystem resources (organic fertilizer) with nature-based solutions, representing a circular economy approach and sustainable management of contaminated biomass. (2) Methods: Six treatments were established to produce compost; closed-system plastic composters were used, with a capacity of 15 kg of biomass and organic waste, consisting of contaminated and uncontaminated biomass of macrophytes with Hg and fruit and vegetable waste (fruit and vegetable waste, pruning waste, and poultry manure). The concentrations of As and total and bioavailable Hg were monitored during the composting process by atomic absorption spectroscopy and so were properties such as pH; electrical conductivity; temperature; CO, TN, S, and SiO2 contents; and C/N ratio. (3) Conclusions: The concentrations of bioavailable Hg during the composting process were between 658.1 and 1.2 µg/kg, decreasing in the following order: T-2 > T-3 > T-1 > C-3 > C-2 > C-1. Composting in the treatments was shown to be an efficient bioremediation technique, as all of the treatments reduced the bioavailability of Hg to below 1.5%, and the physicochemical properties of pH (r: −0.3675; p < 0.007) and %S content (r: −0.6303; p < 0.0025) showed a significant moderate negative correlation with bioavailable Hg concentrations, playing a crucial role in reducing the bioavailability of Hg during the purification process of composting. The results show that all treatments significantly reduced Hg bioavailability below 1.5%; however, T-2 proportionally showed the highest reductions during the process. Compost production was proven to be a sustainable strategy for the management of biomass contaminated with mercury, which is very important for recovering ecosystem services in communities.

1. Introduction

Globally, heavy metals are found naturally in ecosystems and soils; however, due to the increase in human activities and development, they are used in anthropogenic activities, such as mining and smelting industries, metal processing, chemical industry, industrial production, smelting, electroplating, and use of pesticides and fertilizers [1]. In general, heavy metals have become a global environmental problem due to the generation of pollution and accumulation in ecosystems [2,3]. These metals can be transformed from the aqueous phase to the solid phase through adsorption, complexation, coprecipitation, and ion exchange and, sometimes, they are stored in sediments [4]. Due to anthropogenic activities worldwide, 28,400 to 94,000 tons of arsenic (As) and 1108 to 3784 t of mercury (Hg) are released into soil [5]. Hg predominates in its elemental form Hg(0), in sulfide minerals (metacinnabar β-HgS), chlorides, inorganic and organic Hg(II), and methylmercury (MeHg) [6], while, for As, the predominant forms are the inorganic forms, which include arsenate (As(V)) and arsenite (As(III)) [7]. These two metals are characterized by their high toxicity, long persistence, and low biodegradability in the environment, and they can accumulate in crops and enter the human body through the food chain [5]. A total of 37–37.7% of Hg released into the environment globally comes from artisanal small-scale gold mining (ASGM), with 675–1000 metric tons yr−1; in Latin America, 40.6% (340 tons) of these Hg emissions are due to this mining activity [8]. For this reason, it is important to understand the transformation of Hg through treatment processes to control the ecological risks of contamination [9] through strategies that allow for the elimination or immobilization of heavy metals in the soil by means of organic and inorganic additives. From this point of view, composting is an effective alternative because it has been used as a highly effective amendment for heavy metals because it has the ability to reduce the fraction of mobile and exchangeable metals in contaminated soil [10]. In addition, this bioremediation technology is very ecological, cheap, favorable, easy to implement, and very effective compared with other conventional technologies [4]. The composting formation process includes a series of mechanisms for immobilizing and reducing the bioavailability of heavy metals, such as chemical adsorption reactions, precipitation, surface precipitation, ion exchange, redox reaction, and stable complex formation [3]. These effects strengthen the adsorption stability of heavy metals in soil and cause metals to shift from highly bioavailable heavy metal species to the organic and residual fraction with low mobility and availability [11]. The composting process does not reduce the concentration of metals such as Hg but their bioavailability, where the increase in humification and the activity of specific microorganisms are predominant, which is important to avoid the entry of heavy metals into the food chain and the risk to human health [12,13,14]. During the composting process, some physicochemical parameters, such as pH, humic substances, and organic carbon, can affect the bioavailability of heavy metals [15]. Composting is essential to managing municipal and agricultural organic waste, and it is important in the recycling of nutrients, which is important for soil fertility, food production, and environmental sustainability [16]. In addition, it contributes to circular economy processes, promoting the conservation and generation of ecosystem services, based on the sustainable management of areas affected by gold mining. There are research reports that demonstrate the behavior of the bioavailability and mobility of heavy metals such as Hg during the composting process using various organic materials [13,14,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54]. In Colombia, research has been carried out to reduce the bioavailability of heavy metals (Cd, As, Pb, and Hg) in soils using organic amendments and experiments with Lactuca sativa L. [18,19]. In this country, there are many ecosystems affected by Hg contamination due to ASGM, where composting could be an effective alternative to reduce the bioavailability of Hg in arable soils and in the food chain of these ecosystems. ASGM in the district of San Juan in the Chocó region (Colombian Pacific) has generated hundreds of abandoned puddles since the last century (1997), some of which have been abandoned for more than 20 years; there are reports of significant concentrations of Hg in macrophyte plant species that have developed over time in these puddles [13,17,18,19,20]. These abandoned puddles have generated ecosystem resources for residents of the area for years. However, no research has been carried out on reducing the bioavailability of Hg present in these ecosystems and making the latter safe for the health of the inhabitants to generate ecosystem services. In relation to the above, the objectives of this research study are to (1) take advantage of the plant biomass of these puddles to produce compost as a bioremediation strategy, reducing the bioavailability of Hg and, thus, making compost a sustainable alternative to organic fertilizer; (2) monitor Hg and As concentrations and physicochemical properties important for the bioavailability of Hg during the composting process; and (3) determine which treatments (organic waste) are the most efficient in the production of compost with bioremediation properties.

2. Materials and Methods

2.1. Study Area

This study was carried out in the municipality of Unión Panamericana; the point where the experimental design was set up is geographically located at the following co-ordinates: N 5°15′49.3272″ W 76°38′17.5128″, in the San Juan Mining District (Chocó Department) in eastern Colombia (Figure 1). The region is dominated by the Afro-Colombian and indigenous population and the municipality of Unión Panamericana is bordered by the Atrato River, a basin highly impacted by small-scale artisanal gold mining. This municipality has an average annual rainfall of 6500 mm, altitude of 119 m, and the “driest” months are January, February, March, and December and the wettest months are between April and November [13]. According to IDEAM (Institute of Hydrology, Meteorology and Environmental Studies-Colombia), average annual maximum temperatures range between 33.8 °C and 34.9 °C and minimum temperatures between 20.7 °C and 22.0 °C [21]. According to the Köppen–Geiger index, there is a rainy, humid tropical, rainforest equatorial climate that is characterized by high temperatures and its average annual temperature is 27 °C [22]. Geologically, it is a region with high gold and platinum content, which is related to the incessant gold mining activities that date back to the 18th century and are currently the basis of the economy for most of the inhabitants [23].

2.2. Sample Collection

The macrophyte plants for the treatments were collected in three abandoned puddles in the municipality of Unión Panamericana (Chocó, Colombia), which have been generated by small-scale artisanal gold mining, located at the following co-ordinates: pond # 1, N 05°17′1.7″ W 76°39′50.7″; pond # 2, N 05°17′51.2″ W 76°41′00.9″; puddle # 3, N 05°17′46.9″ W 76°39′49.5″ (Figure 1). Puddles 1 (0.64 ± 0.57 µg g−1) and 2 (0.20 ± 0.18 µg g−1) were chosen because they had the highest Hg levels in sediments and macrophyte plants (biomass underground: 0.55 µg g−1; aboveground: 0.15 µg g−1), while puddle 3 (0.07 ± 0.00 µg g−1) was chosen as a control because of the lowest Hg concentrations [20,24]. For the collection, float trips were made parallel to the edge of the puddles. Poultry manure was obtained fresh from a local chicken coop, fruit and vegetable waste was collected from two markets in the municipality, and the pruning waste consisted mainly of fresh weed clippings collected from the site where the experimental process was carried out.

2.3. Sample Analysis

A total of 0.5 g dry weight of the plant samples (macrophytic plants, pruning remains, fruits and vegetables, and compost) and poultry manure were subjected to microwave-assisted digestion (Milestone ETHOS TOUCH series 127697, Sorisole, Italy) using a HNO3/H2O2 acid mixture (5:2 v/v), with a temperature control range of 100–175 °C and a pressure of 1500 kPa [25]. All total mercury (THg) analyses were performed by cold vapor atomic absorption spectroscopy (CV-AAS) using a Thermo Scientific iCETM 3500 Series analyzer (Waltham, MA, USA).
Total As analysis was performed by calcining a mixture of 1 g of each plant material sample with Mg (NO3)2 at 550 °C in a muffle furnace, then adding 1 mL of concentrated HNO3 and heating to dryness, then diluting with 4.5 N HCl, filtering (0.45 μm filter), and then making it up to 25 mL with distilled water [26]. For the analysis of As (HGAAS; standard methods SM 3114, 2017), a Hydride Generation Atomic Absorption Spectroscopy (HG-AAS) (Thermo Scientific iCETM 3500 AAS) was used, coupled to a VP100 continuous flow steam generator (Waltham, MA, USA). The recovery percentage was between 90 and 110% and the detection limits for the different metals were 27.77 μg g−1 for As and 0.73 μg g−1 for Hg and the calibration curves showed R2 values greater than 0.995.

2.4. Analysis of Bioavailability of Hg During the Composting Process

The extraction of bioavailable Hg was performed on the pulverized compost samples (in a ball mill) and weighed in duplicate (1 g) in a 125 mL Erlenmeyer flask and subsequently extracted with a 0.01 M CaCl2 solution [27]. The extraction was performed in a mechanical shaker at 250 rpm for two hours. Then, it was centrifuged; we took the supernatant and filtered it in plastic funnels with Watman paper in 25 mL volumetric flasks; then, the content was transferred to plastic vials and refrigerated at 4 ° C. Three reagent blanks were prepared with the same conditions as the samples for quality control of the method. Mercury readings were performed in an atomic absorption spectrometer (Thermo Electron Corporation, ICE-3500 with air-acetylene flow, acetylene/nitrous oxide, and Zeeman corrector) with graphite furnace mode [55] (United States Environmental Protection Agency, 1997).

2.5. Quality Assurance

The analytical method used to determine THg TAs concentrations in plant materials was validated with a certified reference material “Estuary sediment” (IAEA-405, T-Hg = 810 ng/g, dw) and a triplicate evaluation for quality control of the methods used. The recovery percentage was between 90 and 110% and the detection limits for the different metals were 0.73 μg/kg for Hg and 27.77 μg/kg for As.

2.6. Analysis of Physicochemical Properties of Composting

The temperature (°C) during the composting process was determined in situ; this was carried out every 8 days for 6 months and was carried out with a field thermometer for soils and composting (Reotemp Compost, San Diego, CA, USA); likewise, the pH and electrical conductivity (EC) were also measured in situ in a 1:5 (w/v) suspension of compost in distilled water. The samples were added to 50 mL centrifuge tubes, shaken manually for one minute, left to rest for another minute, and then used for pH measurement with a pH meter (HI 2020, Hanna Instruments Inc., Vainilla, Col. Granjas México, Ciudad de México, Mexico) and, for conductivity, a portable conductivity meter was used (EC/TDS/Temp, Hanna Instruments Inc., Vainilla, Col. Granjas México, Ciudad de México, Mexico). Organic nitrogen was determined using the Kjeldahl method [28], silicon content was separated by wet mineralization and analyzed by atomic absorption spectroscopy, organic carbon was determined by the Walkley–Black method [29], and cation exchange capacity was determined by the Wenk and Bulakh method [30].

2.7. Experimental Design

To evaluate the bioremediation capacity during compost production, three treatments and three closed compost controls of 15 kg each (wet weight of materials) were established in plastic containers, which contained black plastic inside, with dimensions of 0.32 m × 0.27 m × 0.30 m (length × width × height). All treatments had a 3:1 ratio. T-1: contaminated macrophyte plants/poultry manure; T-2: contaminated macrophyte plants/fruit and vegetable waste; T-3: contaminated macrophyte plants/pruning waste; C-1: uncontaminated macrophyte plants: poultry manure; C-2: uncontaminated macrophyte plants/fruit and vegetable waste; C-3: uncontaminated macrophyte plants/pruning waste. The experiment was carried out with three replicates per treatment and three repetitions for 6 months. The compost was turned twice a week, every 4 days, to maintain good ventilation and sufficient oxygen from the mesophilic phase until reaching the compost maturation phase. Humidity control was carried out by removing leachates and solar exposure of the treatments. In addition, using a Lumex RA-915AM mercury analyzer (Mission, BC, Canada), every 15 days in the area of the composting units, Hg monitoring in the air was carried out to estimate its possible volatilization.

2.8. Statistical Analysis

An experiment was carried out with six simple treatments, three with Hg-contaminated macrophyte biomass and three with uncontaminated biomass as a control to evaluate the effectiveness of composting in reducing Hg bioavailability. The results are presented as median ± standard deviation of nine determinations. After assessing normality using the Shapiro–Wilk test and homogeneity of variance using the Bartlett test, the data were subjected to one- or two-way ANOVA in comparisons between treatments at different times for pH, electrical conductivity, temperature, and Hg bioavailability; a comparison of means was performed using the Bonferroni test and Tukey’s multiple comparisons test; in addition, each treatment was compared with its respective control, as well as comparisons between treatments. In addition, the relationship and Spearman’s correlation between physicochemical properties and bioavailable Hg concentrations was assessed. For all analyses, the statistical software GraphPad PRISM version 9.3.1 was used. A p-value of 0.05 was chosen to indicate statistical significance.

3. Results and Discussion

3.1. Comparison of Compost Properties in Different Treatments

Table 1 summarizes the main properties of the six treatments obtained in the composting process after six months, which showed significant differences. In general, the compost produced in the different experimental treatments showed changes in temperature (°C), potential hydrogen (pH), cation exchange capacity (CEC), electrical conductivity (EC), total nitrogen (TN), carbon/nitrogen ratio (C/N), and the contents of CO (oxidizable organic carbon), SiO2 (silicon), and S (sulfur). The changes experienced in temperature in the composting process are shown in Figure 2A. The highest temperatures were reached after 3–6 weeks, at 52.2 °C; this would correspond to the thermophilic phase of the composting process and where the maximum degradation process of organic matter would take place [31]. In general, the minimum temperature was 24 °C and the maximum 52.2 °C; the highest values were observed in all treatments in the second month and were significant with respect to the other months of the process (p < 0.05). However, these temperatures were lower than those observed in the works of Chen et al. [4], with approximately 68 °C, Guo et al. [17], with 61 °C, and Maturi et al. [32], with 58 °C. Low temperatures in the treatments are closely related to the relative humidity (90%) of the area and annual rainfall (6500 mm/year) [21]. Unión Panamericana (Colombian Pacific) has a cool season from May to December, with minimum temperatures of 24 °C and maximum of 28 °C, with October being the coldest month (our experiment was carried out between October and March); on average, it rains every day and maintains a relative humidity above 90% [33,34]. The pH in the treatments showed acid–alkaline values, between 6.9 and 8.7, which could be one of the important factors in the drastic reduction in Hg bioavailability in this research. This behavior has been reported in research carried out with winter wheat (Triticum aestivum L.), grown in Hg-contaminated soils in greenhouses, in which negative correlations (p < 0.05) were observed between bioavailable HgT and pH of the soil used [35]. The treatments T-1, T-2, C-1, and C-2 showed higher values than the remaining treatments (p < 0.05) (Figure 2B). The pH could play an important role in the bioavailability of metals in compost, as well as in the growth and metabolism of microbial organisms; a pH of 6–9 is optimal for microbial activities (oxidation reactions, formation of sulfides, methylation and demethylation of Hg, proteolysis, nitrification, fermentation, hydrolysis, lipolysis, oxidation and reduction of sulfur, and humification, among others) and decreasing the available fraction of heavy metals such as Hg [36,37,38,39]. The bacterial phyla in the composting process that have been reported in these pH ranges are Firmicutes, Actinobacteria, Proteobacteria, Bacteroidetes, and Chloroflexiphylum; fungi are Ascomycota, Basidiomycota, and the subphylum Mucoromycotina; and yeast species are of the orders Saccharomycetales and Tremellales [35,40]. In this research, all treatments are within this pH range; in addition, all the treatments showed significant values between the beginning and end of the composting process: C-1 (from 6.9 to 8.5), C-2 (from 7.0 to 7.9), C-3 (from 7.0 to 7.9), T-1 (from 7.3 to 8.7), T-1 (from 7.2 to 8.5), and T-3 (from 6.9 to 7.6) (Figure 2B). Reports from other research show similar pH values in the initial stages of composting [4,19,31,40], which could be related to ammonification and mineralization of organic nitrogen [41]. The total nitrogen in our experiments ranged between 0.785 and 0.870% (weight dry) (Table 1). These values are within those established for mature composting (0.7–1%) and are similar to the experiments carried out by Al-Bataina et al. [42] and Tibu et al. [43]. Overall, the C/N ratio in compost showed values between 14 and 16, with T-2 and T-3 being the highest; these reports are higher than those observed in recent studies evaluating composting [39]. Research carried out by various authors shows a significant decrease in the C/N ratio during the behavioral process, with average values of 20 [4,44,45,46]. The composting maturation process is related to the decrease in the C/N ratio, which indicates a reduction in carbon content due to microbial activities and an increase in nitrogen [43]. The CO values in the treatments after the composting process reported values between 11.2 and 13.1% (weight dry); T-3 showed the highest value in contrast to C-2. This could be related to the high amounts of ligocellulosic material present in the pruning remains, the contaminated macrophyte biomass, and possible higher amounts of organic Hg, unlike the other treatments. These results agree with the optimal values established [45] and are similar to works carried out by Tibu et al. [43] and Kharter [46] and lower than the reports by Chen et al. [15]. On the other hand, the CECs in general showed similar values in most of the treatments (32.5–39.5), except T-2 (61.1 meq/100 g), which showed a remarkably higher amount (p < 0.05). The CEC represents the negative charge that exists on the surfaces of clay and organic matter; it is a very important property because it is a property that demonstrates the capacity of compost to absorb cations of heavy metals [47]. CEC explains the affinity adsorption of heavy metals by iron oxide and carbonate compounds, which are present in compost [48]. Thus, CEC could explain the reduction in heavy metal bioavailability during composting in this research [17]. In agreement with the above, our reports agree with the results obtained by Guo et al. [17]. However, no statistically significant relationship was found between the CEC and the concentrations of bioavailable Hg. EC is a property that determines the concentration of soluble salts in compost; the EC values decreased in the following order: T-1 < C-1 < T-2 < C-2 < T-3 < C-3 (p < 0.05). In our research, the average EC value was 1275.2 μS/cm for T-1, which was the highest of all treatments, showing significant differences with all treatments, except C-1 at month 0; C-1, C-2, and T-2 at month 2; and with all in months 4 and 6 (Figure 2C). Treatment C-3 reported the lowest values, with an average of 431.4 μS/cm. In general terms, the EC values were low compared to the reports by Nartey [49], Rashad et al. [50], Chen et al. [4], Maturi et al. [32], and Sardroudi et al. [39]. However, these values are below the maximum limit of 4000 μS/cm, which is necessary to maintain plant growth and remedy saline soils [51]. The contents of SiO2 and S are another important property that could have played an important role in the reduction in the bioavailability of Hg in the composting treatments; these reported values from 4.86 to 19.0 for SiO2 (p < 0.05) and 0.12 to 0.23 for S. Although the sulfur contents were low, the SiO2 values were high, especially in T-2 (p < 0.05), followed in order by T-1 and T-3.

3.2. Concentration of Hg and As in the Treatments During the Composting Process

Bonferroni and Tukey tests and one-way ANOVA were used for the variation in total amounts of Hg and As, and the results showed significant changes in the total contents of these heavy metals (p < 0.05) during the composting process in all treatments. The concentrations of Hg in the treatments ranged from 47.2 to 802.5 µg kg−1; these concentrations increased in the following order: C-1 > C-2 > C-3 > T-1 > T-3 > T-2 (Figure 3A). The highest concentrations were observed at 6 months in all treatments due to the drastic reduction in biomass of the organic materials used for composting, water loss, and CO2 (Figure 3A). Treatments T-2 and T-3 showed significantly higher concentrations of Hg during the composting process compared to the other treatments (p < 0.05); likewise, T-1 and C-3 showed high concentrations at 4 and 6 months (p < 0.05), compared to months 0 and 2 (Figure 3A). On the other hand, C-1 and C-2 showed the lowest concentrations compared to the other treatments in months 0, 4, and 6 (p < 0.05, Figure 3A). These results are similar to experiments on composting produced from sludge and rural organic solid waste [52,53]. However, in some composts produced from sewage sludge, there was a nonsignificant decrease in Hg concentrations during composting [54,56].
Surprisingly, the treatments reported high concentrations of As (Figure 3B); in other research in fish, fruits, and vegetables in the Atrato River basin, variable concentrations of this metal were observed [57,58]. The communities inhabiting these areas close to the basin from Río Atrato have an agricultural vocation; therefore, they have used for many years fertilizers (now, they use compost more as organic fertilizer from manure from farm animals and vegetable remains), insecticides, pesticides, and herbicides for their crops. These agrochemicals contain trace amounts of arsenic and most of them are As(V) compounds, with some As(III) compounds, for example, calcium arsenite and copper acetoarsenite-Paris Green as pesticides and methyl arsenic acid and dimethyl arsenic acid as herbicides [59,60]. Also, feed additives for poultry and pigs, such as roxarsone (C6AsNH6O6) and p-arsanilic acid (C6H8AsNO3), are used to increase body weight and to treat and prevent diseases [59,60]. Thus, the use of animal excrement as organic fertilizer could explain how As can enter crops [61].
These concentrations were significantly higher than those of Hg in months 2, 4, and 6 (p < 0.05, Figure 3B). The concentrations of As ranged between 797.8 and 2844.5 µg/kg. AsT-2 reported the highest concentrations in the first 4 months (p < 0.05), showing significant differences with the other treatments in month 2, with AsC-1 and AsC-3 in month 4, and with AsC-2 and AsC-3 in month 6. Likewise, in AsC-1, the highest concentrations were observed at 6 months (p < 0.05). These drastic changes in As concentrations were also observed in experiments carried out by Xu et al. [53] in rural solid waste composting, where initial concentrations of 23.68 mg/kg and final concentrations of 131.80 mg/kg were reported.

3.3. Bioavailability of Hg in the Experimental Treatments During the Composting Process

The bioavailable concentrations of Hg during the composting process in each of the treatments showed a drastic reduction in the second month of the experiment (p < 0.05, Figure 4A). The compost formation reduced the bioavailability of Hg to less than 1.4% of the initial concentrations (Figure 4B). The concentrations of Hg during the composting process were between 658.1 and 1.2 µg/kg. These concentrations decreased in the following order: T-2 > T-3 > T-1 > C-3 > C-2 > C-1. The lowest bioavailable concentrations of Hg were observed in C-1, C-2, and C-3, in that order, respectively. On the other hand, T-2 presented the highest concentrations (p < 0.05). However, after 6 months, all treatments showed concentrations between 7.5 and 1.2 µg/kg, between 0.7 and 1.4% with respect to the initial Hg concentrations (Figure 4A,B). In T-2, the greatest decreases in bioavailable Hg were observed, showing significant reductions in all months (p < 0.05).
These results show a much lower percentage reduction than the experimental data of Xu et al. [53]; however, those were similar to the reports for Janowska et al. [52]. The amount of organic matter (in the form of organic carbon and nitrogen) translated into the formation of many organic compounds that bind to Hg contributed to the drastic reduction in the bioavailability of Hg [14]. Furthermore, there are reports stating that sulfur and silicon can change the speciation of heavy metals and reduce their bioavailability to plants [62]; likewise, CEC, CO, and pH reduction surely also played a key role in the reduction in Hg bioavailability in the different composting treatments of our experiment [32,39]. The thermophilic phase (includes an increase in temperature in the composting) between 3 and 6 weeks into the composting coincides with a significant increase in pH values in all treatments, an increase in electrical conductivity in T-2 and C-2, and a significant decrease in the bioavailability of Hg (p > 0.05) in all treatments. This could be closely related to the microorganisms active in this phase in the decomposition of organic matter and reduction of Hg (II) to Hg (0) [14,63]. Likewise, the reduction in bioavailable Hg observed is this research could be related to the production of HgS during the composting process. It is known that this process includes mesophilic and thermophilic methanogenic phases, characterized by prolonged high temperatures due to the extensive metabolic activities carried out by endogenous microorganisms (Actinobacteria, Archaea, Bacteroidetes, Desulfobacterota, Euryarchaeota, Nitrospirae, etc.) [13,64]. Hg methylation and MeHg demethylation are related to metabolic processes such as sulfate/iron reduction and methanogenesis, both processes related to the activity of Desulfobacterota and Euryarchaeota species, respectively [13,65]. This microbial metabolic process from sulfur and organic matter generates sulfides, which can react with Hg (II) to generate HgS, thus reducing the bioavailability of Hg(II) [13].
The importance of these properties on Hg bioavailability was supported by statistical analysis. In this research, Spearman correlation and simple linear regression analyses performed between these properties and bioavailable Hg concentrations during the composting process in all treatments showed statistical significance (p < 0.05). A low positive correlation was observed between bioavailable Hg concentrations in compost (Hg-B) and electrical conductivity (EC) (r: 0.30; p < 0.0035), with a moderate negative correlation with pH (r: −0.3675; p < 0.007) and %S (r: −0.6303; p < 0.0025) (Figure 5A–C). Furthermore, a moderate, significant positive correlation was observed for total Hg concentrations (r: 0.389; p < 0.004) and temperature (r: −0.3670; p < 0.0025) (Figure 5F,I). The other correlations were very weak, positive or negative, but without statistical significance (Figure 5). However, R2 levels were low, the highest being %S, explaining 32% of the variability in bioavailable Hg concentration in compost, followed by only 11% for CEC and HgT. The S content in amendments has been used to reduce Hg bioavailability by forming insoluble and less available forms of Hg-S or Hg-SH [65,66,67,68]. Likewise, the generation of sulfides in the thermophilic phase can contribute to the reduction in Hg bioavailability as mentioned above [13]. The results suggest that there is a synergy between these physicochemical properties during the composting process that has allowed a significant reduction in the content of bioavailable Hg, demonstrating that this process is a sustainable strategy for the management of biomass contaminated with Hg.

4. Conclusions

For the first time, the production of compost from biomass of macrophyte plants contaminated with Hg from ASGM-generated ponds is reported as an ecological, sustainable strategy to bioremediate these ecosystems. Hg and As concentrations during the composting process showed a significant increase, with As concentrations being the highest. This research showed that all treatments significantly reduced Hg bioavailability below 1.5% once the composting process was finished. However, T-2 showed proportionally the highest reductions in bioavailable Hg during the process. These results are closely related to the physicochemical properties observed in the treatments; an increase in the pH value was observed, which is related to the reduction in bioavailable Hg (r: −0.3675; p < 0.007). Likewise, the %S content showed the highest correlations (r: −0.6303; p < 0.0025), which could be key in this process because it is involved in the production of sulfides in the thermophilic phase, which could generate HgS, thus reducing the bioavailable Hg in the compost. In addition, the R2 of %S content showed a prediction of the variability of bioavailable Hg concentrations by 32%. This suggests that physicochemical properties together played a crucial role in reducing Hg bioavailability. The experiments demonstrated that composting is a valuable strategy to reduce Hg pollution in areas degraded by gold mining activities, which is important to recover ecosystem services in these communities.

Author Contributions

M.S.-M. performed the experiments, data/evidence collection, and writing—review and editing of the initial draft; G.R.-M. performed the experiments, data/evidence collection, and performed the critical review; H.G.-P. performed the critical review, commentary, and revision for the pre-publication stage; Y.P.-T. provided oversight and leadership responsibility for the research activity’s planning and execution; A.R.-P. performed the experiments, data/evidence collection, and performed the critical review; J.M.-N. developed and designed the methodology for plant growth under greenhouse conditions, formulated the evolution of the overarching research goals and aims, provided reagents, materials, instrumentation, and computing resources for mass spectrometry analysis, and performed the critical review, commentary, and revision for the pre-publication stage. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the project code 2020000100055 contract 569, financed by the Ministry of Science, Technology, and Innovation (Minciencias), through the General Royalties System(SGR); funding was received from the University of Córdoba project FCB-01-19 and FCB-01-22.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article. All figures and tables in this manuscript were originally created by us as a result of this article and can be used without copyright restrictions.

Acknowledgments

The authors are grateful to the members of the Laboratory of Toxicology and Environmental Management of the University of Córdoba (Colombia), the Analytical Chemistry and Biomedicine Group, and especially to the Biosistematic Research Group of the Technological University of Chocó (Colombia). We also thank Minciencias, the Technological University of Chocó ‘DLC’, and the University of Córdoba for financing this project.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Adnan, M.; Xiao, B.; Xiao, P.; Zhao, P.; Li, R.; Bibi, S. Research Progress on Heavy Metals Pollution in the Soil of Smelting Sites in China. Toxics 2022, 10, 231. [Google Scholar] [CrossRef] [PubMed]
  2. Kumari, S.; Amit, R.J.; Mishra, N.; Singh, D.K. Recent developments in environmental mercury bioremediation and its toxicity: A review. Environ. Nanotechnol. Monit. Manag. 2020, 13, 100283. [Google Scholar] [CrossRef]
  3. Chen, Y.; Ma, S.; Li, Y.; Yan, M.; Zeng, G.; Zhang, J.; Zhang, J.; Tan, X. Microbiological study on bioremediation of 2,2‚Ä≤,4,4‚Ä≤-tet bromodiphenyl ether (BDE-47) con- taminated soil by agricultural waste composting. Appl. Microbiol. Biotechnol. 2017, 100, 9709–9718. [Google Scholar] [CrossRef] [PubMed]
  4. Chen, X.; Zhao, Y.; Zeng, C.; Li, Y.; Zhu, L.; Wu, J.; Chen, J.; Wei, Z. Assessment contributions of physicochemical properties and bacterial community to mitigate the bioavailability of heavy metals during composting based on structural equation models. Bioresour. Technol. 2019, 289, 121657. [Google Scholar] [CrossRef]
  5. Wei, Y.; Li, R.; Lu, N.; Zhang, B. Stabilization of Soil Co-Contaminated with Mercury and Arsenic by Different Types of Biochar. Sustainability 2022, 14, 13637. [Google Scholar] [CrossRef]
  6. Gilli, R.; Karlen, C.; Weber, M.; Rüegg, J.; Barmettler, K.; Biester, H.; Boivin, P.; Kretzschmar, R. Speciation and Mobility of Mercury in Soils Contaminated by Legacy Emissions from a Chemical Factory in the Rhône Valley in Canton of Valais, Switzerland. Soil Syst. 2018, 2, 44. [Google Scholar] [CrossRef]
  7. Gao, M.; Su, Y.; Gao, J.; Zhong, X.; Li, H.; Wang, H.; Lü, C.; He, J. Arsenic speciation transformation in soils with high geological background: New insights from the governing role of Fe. Chemosphere 2022, 302, 134860. [Google Scholar] [CrossRef]
  8. UN Environment. Global Mercury Assessment 2018; UN Environment Programme, Chemicals and Health Branch: Geneva, Switzerland, 2019; 62p. [Google Scholar]
  9. Xiang, Y.; Zhu, A.; Guo, Y.; Liu, G.; Chen, B.; He, B.; Liang, Y.; Yin, Y.; Cai, Y.; Jiang, G. Decreased bioavailability of both inorganic mercury and methylmercury in anaerobic sediments by sorption on iron sulfide nanoparticles. J. Hazard. Mater. 2022, 424, 127399. [Google Scholar] [CrossRef]
  10. Tang, J.; Zhang, L.; Zhang, J.; Ren, L.; Zhou, Y.; Zheng, Y.; Luo, L.; Yang, Y.; Huang, H.; Chen, A. Physicochemical features, metal availability and enzyme activity in heavy metal-polluted soil remediated by biochar and compost. Sci. Total Environ. 2020, 701, 134751. [Google Scholar] [CrossRef]
  11. Wang, F.; Yao, W.; Zhang, W.; Miao, L.; Wang, Y.; Zhang, H.; Ding, Y.; Zhu, W. Humic acid characterization and heavy metal behaviour during vermicomposting of pig manure amended with 13C-labelled rice straw. Waste Manag. Res. 2022, 40, 736–744. [Google Scholar] [CrossRef]
  12. Chen, Y.; Liu, Y.; Li, Y.; Wu, Y.; Chen, Y.; Zeng, G.; Zhang, J.; Li, H. Influence of biochar on heavy metals and microbial community during composting of river sediment with agricultural wastes. Bioresour Technol. 2017, 243, 347–355. [Google Scholar] [CrossRef] [PubMed]
  13. Liu, J.; Bao, Z.; Wang, C.; Wei, J.; Wei, Y.; Chen, M. Understanding of mercury and methylmercury transformation in sludge composting by metagenomic analysis. Water Res. 2022, 226, 119204. [Google Scholar] [CrossRef]
  14. Yang, H.I.; Lou, K.; Rajapaksha, A.U.; Ok, Y.S.; Anyia, A.O.; Chang, S.X. Adsorption of ammonium in aqueous solutions by pine sawdust and wheat straw biochars. Environ. Sci. Pollut. Res. 2018, 25, 25638–25647. [Google Scholar] [CrossRef] [PubMed]
  15. Chen, Y.; Chen, Y.; Li, Y.; Liu, Y.; Zhang, D.; Wu, Y.; Li, H.; Xu, F.; Li, M. The Effect of Composting on the Multiple Heavy Metals in the River Sediment Investigated by Multivariate Analysis. Water Air Soil Pollut. 2021, 232, 20. [Google Scholar] [CrossRef]
  16. Manea, E.E.; Bumbac, C.; Dinu, L.R.; Bumbac, M.; Nicolescu, C.M. Composting as a Sustainable Solution for Organic Solid Waste Management: Current Practices and Potential Improvements. Sustainability 2024, 16, 6329. [Google Scholar] [CrossRef]
  17. Guo, H.-N.; Wang, L.-X.; Liu, H.-T. Potential mechanisms involving the immobilization of Cd, As and Cr during swine manure composting. Sci. Rep. 2020, 10, 16632. [Google Scholar] [CrossRef]
  18. Martínez-Madrid, D.E.; Marrugo-Negrete, J. Effects of adding amendments on the immobilization of heavy metals in mining soils of southern Bolívar, Colombia. Cienc. Tecnol. Agropecu. 2021, 22, e2272. [Google Scholar]
  19. Rivera, J.; Reyes, J.; Cuervo, J.; Martínez-Cordón, M.; Zamudio, A. Effect of biochar amendments on the growth and development of ‘Vera’ crisp lettuce in four soils contaminated with cadmium. Chil. J. Agric. Res. 2022, 82, 244–255. [Google Scholar] [CrossRef]
  20. Gutiérrez-Mosquera, H.; Marrugo-Negrete, J.; Díez, S.; Morales-Mira, G.; Montoya-Jaramillo, L.J.; Jonathan, M.P. Distribution of chemical forms of mercury in sediments from abandoned ponds created during former gold mining operations in Colombia. Chemosphere 2020, 258, 127319. [Google Scholar] [CrossRef]
  21. PDUP. Plan de Desarrollo Municipio de Unión Panamericana—Comprometidos con el Cambio para Servir 2020—2023—Alcaldía Municipal de Unión Panamericana Chocó. 2020. Available online: https://www.unionpanamericana-choco.gov.co/normatividad/plan-de-desarrollo-municipio-de-union-panamericana-comprometidos (accessed on 14 August 2024).
  22. Beck, H.E.; Zimmermann, N.E.; McVicar, T.R.; Vergopolan, N.; Berg, A.; Wood, E.F. Present and future Köppen-Geiger climate classification maps at 1-km resolution. Sci. Data 2018, 5, 180214. [Google Scholar] [CrossRef]
  23. PMGRD. Plan de Gestión del Riesgo de Desastres del Municipio de Unión Panamericana-Chocó. 2020–2023—Alcaldía Municipal de Unión Panamericana Chocó. Available online: https://www.unionpanamericana-choco.gov.co/normatividad/plan-de-gestion-del-riesgo-de-desastres-del-municipio (accessed on 14 August 2024).
  24. Gutiérrez-Mosquera, H.; Marrugo-Negrete, J.; Díez, S.; Morales-Mira, G.; Montoya-Jaramillo, L.J.; Jonathan, M.P. Mercury distribution in different environmental matrices in aquatic systems of abandoned gold mines, western Colombia: Focus on human health. J. Hazard. Mater. 2020, 404, 124080. [Google Scholar] [CrossRef] [PubMed]
  25. Jedrzejczak, R.; Szteke, B.; Reczajska, W. Mercury determination in food of plant origin by cold vapour atomic absorption spectrometry (CVAAS). Roczniki Panstwowego Zakladu Higieny 1996, 47, 223–230. [Google Scholar] [PubMed]
  26. Szkoda, J.; Zmudzki, J.; Grzebalska, A. Determination of arsenic in biological material by hydride generation atomic absorption spectrometry method. Bull. Vet. Inst. Pulawy 2006, 50, 269–272. [Google Scholar]
  27. Vázquez, F.; Pérez, B.; Río, S. Assessment of metal bioavailability in the vineyard soil-grapevine system using different extraction methods. Food Chem. 2016, 208, 199–208. [Google Scholar] [CrossRef]
  28. Kjeldahl, J. “Neue Methode zur Bestimmung des Stickstoffs in organischen Körpern” (New method for the determination of nitrogen in organic substances). Z. Anal. Chem. 1883, 22, 366–383. [Google Scholar] [CrossRef]
  29. Walkley, A.; Black, I.A. An examination of Degtjareff method for determining soil organic matter and a proposed modification of the chromic acid titration method. Soil Sci. 1934, 37, 29–38. [Google Scholar] [CrossRef]
  30. Wenk, H.R.; Bulakh, A. Minerals. Their Constitution and Origin; University Press Cambridge: Cambridge, UK, 2004. [Google Scholar]
  31. Jain, M.S.; Kalamdhad, A.S. Efficacy of batch mode rotary drum composter for management of aquatic weed (Hydrilla verticillata (L.f.) Royle). J. Environ. Manag. 2018, 221, 20–27. [Google Scholar] [CrossRef]
  32. Maturi, K.C.; Banerjee, A.; Kalamdhad, A.S. Assessing mobility and chemical speciation of heavy metals during rotary drum composting of Ageratum conyzoides. Environ. Technol. Innov. 2021, 24, 101871. [Google Scholar] [CrossRef]
  33. Clima Colombia. 2024. Available online: https://www.clima.com/colombia/choco/las-animas (accessed on 12 August 2024).
  34. Plan de Desarrollo Municipio Unión Panamericana, 2024–2027. Available online: https://www.unionpanamericana-choco.gov.co/noticias/contruccion-del-plan-desarrollo-20242027 (accessed on 12 August 2024).
  35. Hussain, S.; Yang, J.; Hussain, J.; Sattar, A.; Ullah, S.; Hussain, I.; Rahman, S.; Zandi, P.; Xia, X.; Zhang, L. Mercury fractionation, bioavailability, and the major factors predicting its transfer and accumulation in soil–wheat systems. Sci. Total Environ. 2022, 847, 157432. [Google Scholar] [CrossRef]
  36. Li, X.; Shi, X.-S.; Lu, M.-Y.; Zhao, Y.-Z.; Li, X.; Peng, H.; Guo, R.-B. Succession of the bacterial community and functional characteristics during continuous thermophilic composting of dairy manure amended with recycled ceramsite. Bioresour. Technol. 2019, 294, 122044. [Google Scholar] [CrossRef]
  37. Zhang, H.Z.; Guo, Q.J.; Yang, J.X.; Ma, J.; Chen, G.; Chen, T.B.; Zhu, G.X.; Wang, J.; Zhang, G.X.; Wang, X.; et al. Comparison of chelates for enhancing Ricinus communis L. phytoremediation of Cd and Pb contaminated soil. Ecotoxicol. Environ. Saf. 2016, 133, 57–62. [Google Scholar] [CrossRef] [PubMed]
  38. Xiong, R.; Gao, X.; Tu, X.; Mao, Y.; Jiang, L.; Lu, Z.; Du, Y. Heavy metal remediation in sludge compost: Recent progress. J. Renew. Mater. 2022, 10, 469–486. [Google Scholar] [CrossRef]
  39. Sardroudi, N.P.; Sorolla, S.; Casas, C.; Bacardit, A. A Study of the Composting Capacity of Different Kinds of Leathers, Leatherette and Alternative Materials. Sustainability 2024, 16, 2324. [Google Scholar] [CrossRef]
  40. Meng, Q.; Yang, W.; Men, M.; Bello, A.; Xu, X.; Xu, B.; Deng, L.; Jiang, X.; Sheng, S.; Wu, X.; et al. Microbial Community Successionand Response to Environmental Variables During Cow Manure and Corn Straw Composting. Front. Microbiol. 2019, 10, 529. [Google Scholar] [CrossRef]
  41. Zhang, J.; Zeng, G.; Chen, Y.; Yu, M.; Yu, Z.; Li, H.; Yu, Y.; Huang, H. Effects of physico- chemical parameters on the bacterial and fungal communities during agricultural waste composting. Bioresour. Technol. 2011, 102, 2950–2956. [Google Scholar] [CrossRef]
  42. Al-Bataina, B.B.; Young, T.M.; Ranieri, E. Effects of compost age on the release of nutrients. Int. Soil Water Conserv. Res. 2016, 4, 230–236. [Google Scholar] [CrossRef]
  43. Tibu, C.; Annang, T.Y.; Solomon, N.; Yirenya-Tawiah, D. Effect of the composting process on physicochemical properties and concentration of heavy metals in market waste with additive materials in the Ga West Municipality, Ghana. Int. J. Recycl. Org. Waste Agric. 2019, 8, 393–403. [Google Scholar] [CrossRef]
  44. Qian, X.; Shen, G.; Wang, Z.; Guo, C.; Liu, Y.; Lei, Z.; Zhang, Z. Co- composting of livestock manure with rice straw: Characteriza- tion and establishment of maturity evaluation system. Waste Manag. 2014, 34, 530–535. [Google Scholar] [CrossRef]
  45. Batjes, N.H. Total carbon and nitrogen in the soils of the world. Eur. J. Soil. Sci. 1996, 47, 151–163. [Google Scholar] [CrossRef]
  46. Khater, E.S.G. Some Physical and Chemical Properties of Compost. Int. J. Waste Resour. 2015, 5, 72–79. [Google Scholar] [CrossRef]
  47. Sidi, N.; Aris, A.Z.; Talib, S.N.; Johan, S.; Tengku, M. Yusoff, T.S.; Ismail, M.Z. Influential factors on the cation exchange capacity in sediment of merambong shoal, Johor. Procedia Environ. Sci. 2015, 30, 186–189. [Google Scholar] [CrossRef]
  48. Paradelo, R.; Barral, M.T. Evaluation of the potential capacity as biosorbents of two Msw composts with different Cu, Pb and Zn concentrations. Bioresour. Technol. 2012, 104, 810–813. [Google Scholar] [CrossRef] [PubMed]
  49. Nartey, E.G. Faecal Sludge Reuse in Urban and Peri-Urban Crop Production. Master’s Thesis, University of Ghana, Accra, Ghana, 2013. [Google Scholar]
  50. Rashad, F.M.; Saleh, W.D.; Moselhy, M.A. Bioconversion of rice straw and certain agro-industrial wastes to amendments for organic farming systems: 1. Composting, quality, stability and maturity indices. Bioresour. Technol. 2010, 101, 5952–5960. [Google Scholar] [CrossRef] [PubMed]
  51. Diacono, M.; Montemurro, F. Effectiveness of organic wastes as fertilizers and amendments in salt-affected soils. Agriculture 2015, 5, 221–230. [Google Scholar] [CrossRef]
  52. Janowska, B.; Szymański, K.; Sidełko, R.; Siebielska, I.; Walendzik, B. Assessment of mobility and bioavailability of mercury compounds in sewage sludge and composts. Environ. Res. 2017, 156, 394–403. [Google Scholar] [CrossRef]
  53. Xu, S.; Li, L.; Zhan, J.; Guo, X. Variation and factors on heavy metal speciation during co-composting of rural sewage sludge and typical rural organic solid waste. J. Environ. Manag. 2022, 306, 114418. [Google Scholar] [CrossRef]
  54. Cheng, Y.; Yu, Y.; Zhang, C.; Luo, Y.; Zhang, M.; Zhang, Y.; Wang, D. Variation characteristics of mercury during municipal sludge composting and its land use. Environ. Chem. 2021, 40, 2226–2233. [Google Scholar]
  55. United state Environmental Protection Agency. Method 7473 (SW-846). Mercury in Solids and Solutions by Thermal Decomposition, Amalgamation, and Atomic Absortion Spectrophotometry. Methods (1998). Available online: https://www.epa.gov/sites/production/files/2015-07/documents/epa-7473.pdf (accessed on 14 August 2024).
  56. Salazar-Camacho, C.; Salas-Moreno, M.; Marrugo-Madrid, S.; Paternina-Uribe, R.; Marrugo-Negrete, J.; Díez, S. A human health risk assessment of methylmercury, arsenic and metals in a tropical river basin impacted by gold mining in the Colombian Pacific región. Environ. Res. 2022, 212, 113120. [Google Scholar] [CrossRef]
  57. Caicedo-Rivas, G.; Salas-Moreno, M.; Marrugo-Negrete, J. Health Risk Assessment for Human Exposure to Heavy Metals via Food Consumption in Inhabitants of Middle Basin of the Atrato River in the Colombian Pacific. Int. J. Environ. Res. Public Health 2023, 20, 435. [Google Scholar] [CrossRef]
  58. Upadhyay, M.K.; Shukla, A.; Yadav, P.; Srivastava, S. A review of arsenic in crops, vegetables, animals and food products. Food Chem. 2019, 276, 608–618. [Google Scholar] [CrossRef]
  59. Bencko, V.; Foong, F.Y.L. The history of arsenical pesticides and health risks related to the use of Agent Blue. Ann. Agric. Environ. Med. 2016, 24, 312–316. [Google Scholar] [CrossRef] [PubMed]
  60. Geng, A.; Wang, X.; Wu, L.; Wang, F.; Chen, Y.; Yang, H.; Zhang, Z.; Zhao, X. Arsenic accumulation and speciation in rice grown in arsanilic acid-elevated paddy soil. Ecotoxicol. Environ. Saf. 2017, 137, 172–178. [Google Scholar] [CrossRef]
  61. Li, S.; Zheng, X.; Gong, J.; Xue, X.; Yang, H. Preparation of zinc chloride and sulfur modified cornstalk biochar and its stabilizatiom effect on mercury contaminated soil. Chin. J. Environ. Eng. 2021, 15, 1403–1408. [Google Scholar]
  62. Pannu, R.; Siciliano, S.D.; Driscoll, N.J.O. Quantifying the effects of soil temperature, moisture and sterilization on elemental mercury formation in boreal soils. Environ. Pollut. 2014, 193, 138–146. [Google Scholar] [CrossRef] [PubMed]
  63. Papale, M.; Romano, I.; Finore, I.; Lo Giudice, A.; Piccolo, A.; Cangemi, S.; Di Meo, V.; Nicolaus, B.; Poli, A. Prokaryotic Diversity of the Composting Thermophilic Phase: The Case of Ground Coffee Compost. Microorganisms 2021, 9, 218. [Google Scholar] [CrossRef] [PubMed]
  64. Yu, R.Q.; Reinfelder, J.R.; Hines, M.E.; Barkay, T. Syntrophic pathways for microbial mercury methylation. ISME J. 2018, 12, 1826–1835. [Google Scholar] [CrossRef] [PubMed]
  65. Hu, H.; Xi, B.; Tan, W. Effects of sulfur-rich biochar amendment on microbial methylation of mercury in rhizosphere paddy soil and methylmercury accumulation in rice. Environ. Pollut. 2021, 286, 117290. [Google Scholar] [CrossRef]
  66. O’Connor, D.; Peng, T.; Li, G.; Wang, S.; Duan, L.; Mulder, J.; Cornelissen, G.; Cheng, Z.; Yang, S.; Hou, D. Sulfur-modified rice husk biochar: A green method for the remediation of mercury contaminated soil. Sci. Total Environ. 2018, 621, 819–826. [Google Scholar] [CrossRef]
  67. Zhao, B.; O’Connor, D.; Shen, Z.; Tsang, D.C.W.; Rinklebe, J.; Hou, D. Sulfur-modified biochar as a soil amendment to stabilize mercury pollution: An accelerated simulation of long-term aging effects. Environ. Pollut. 2020, 264, 114687. [Google Scholar] [CrossRef]
  68. Hu, H.; Gao, Y.; Tan, W.; Xi, B. Effects of dissolved organic matter on mercury speciation in rice rhizosphere amended with sulfur rich biochar. Soil Environ. Health 2023, 1, 100022. [Google Scholar] [CrossRef]
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Figure 1. Map of sampling sites in the San Juan mining district, Unión Panamericana (A); puddles generated by ASGM activities with high levels of Hg, #1 (B), # 2 (C); puddles with low levels of Hg, # 3 (D).
Figure 1. Map of sampling sites in the San Juan mining district, Unión Panamericana (A); puddles generated by ASGM activities with high levels of Hg, #1 (B), # 2 (C); puddles with low levels of Hg, # 3 (D).
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Figure 2. Temperature behavior during composting production (A), pH variations (B), and electrical conductivity (C) in the treatments during six months in the composting process. TA: ambient temperature of the Municipality Unión Panamerican. Different letters in the same file indicate significant differences between mean values corresponding to different treatment groups (p < 0.05).
Figure 2. Temperature behavior during composting production (A), pH variations (B), and electrical conductivity (C) in the treatments during six months in the composting process. TA: ambient temperature of the Municipality Unión Panamerican. Different letters in the same file indicate significant differences between mean values corresponding to different treatment groups (p < 0.05).
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Figure 3. Behavior of Hg concentrations in the treatments during the composting process (A); As concentrations during six months in the experimental composting treatments (B). AsC-1: As concentrations in C-1, AsC-2: As concentrations in C-2, AsC-3: As concentrations in C-3, AsT-1: As concentrations in T-1, AsT-2: As concentrations in T-2, and AsT-3: As concentrations in T-3. Different letters in the same file indicate significant differences between mean values corresponding to different treatment groups (p < 0.05).
Figure 3. Behavior of Hg concentrations in the treatments during the composting process (A); As concentrations during six months in the experimental composting treatments (B). AsC-1: As concentrations in C-1, AsC-2: As concentrations in C-2, AsC-3: As concentrations in C-3, AsT-1: As concentrations in T-1, AsT-2: As concentrations in T-2, and AsT-3: As concentrations in T-3. Different letters in the same file indicate significant differences between mean values corresponding to different treatment groups (p < 0.05).
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Figure 4. Behavior of bioavailable Hg concentrations in the treatments during the composting process in six months (A); percentage of bioavailable Hg in the experimental composting treatments (B). Different letters in the same file indicate significant differences between mean values corresponding to different treatment groups (p < 0.05).
Figure 4. Behavior of bioavailable Hg concentrations in the treatments during the composting process in six months (A); percentage of bioavailable Hg in the experimental composting treatments (B). Different letters in the same file indicate significant differences between mean values corresponding to different treatment groups (p < 0.05).
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Figure 5. Relationship and Spearman’s correlation between physicochemical properties and bioavailable Hg concentrations during the composting process in all treatments (equation, R coefficient, p-values, and R-square values) (n = 72). (A) Electrical conductivity (EC); (B) pH; (C) contents of sulfur (%S); (D) silicon (SiO2); (E) contents of oxidizable organic carbon (CO); (F) Hg concentrations total; (G) cation exchange capacity (CEC); (H) carbon/nitrogen ratio (C/N); (I) temperature; and (J) total nitrogen (TN). The black line in the figure represents the linear model among variables.
Figure 5. Relationship and Spearman’s correlation between physicochemical properties and bioavailable Hg concentrations during the composting process in all treatments (equation, R coefficient, p-values, and R-square values) (n = 72). (A) Electrical conductivity (EC); (B) pH; (C) contents of sulfur (%S); (D) silicon (SiO2); (E) contents of oxidizable organic carbon (CO); (F) Hg concentrations total; (G) cation exchange capacity (CEC); (H) carbon/nitrogen ratio (C/N); (I) temperature; and (J) total nitrogen (TN). The black line in the figure represents the linear model among variables.
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Table 1. Main properties of the composting treatments obtained.
Table 1. Main properties of the composting treatments obtained.
PropertyTreatments
C-1C-2C-3T-1T-2T-3
Hg Total (μg/kg)130.9 ± 20.9 d180.7 ± 26.8 d353.1 ± 25.2 c350.9 ± 14.2 c802.5 ± 25.1 a660.5 ± 22.1 b
Hg Bioavailable (μg/kg)0.9 ± 0.61.1 ± 0.81.4 ± 0.91.4 ± 0.81.3 ± 0.50.7 ± 0.5
As Total (μg/kg)2844.5 ± 792.7 a748.5 ± 841.5 e1381.0 ± 950.0 d2174.6 ± 310.6 c2699.9 ± 621.0 a2384.4 ± 706.5 b
pH8.5 ± 0.5 a8.3 ± 0.4 a7.9 ± 0.2 b8.7 ± 0.9 a8.5 ± 0.5 a7.6 ± 0.7 b
EC (μS/cm)853.6 ± 105.6 b562.2 ± 49.8 bc491.4 ± 28.2 c1275.2 ± 114.5 a743.2 ± 49.7b c543.2 ± 18.1 bc
S (%)0.12 ± 0.070.19 ± 0.190.23 ± 0.110.14 ± 0.090.14 ± 0.090.15 ± 0.14
SiO2 (%)5.85 ± 0.83 d4.86 ± 0.9 d7.93 ± 0.88 d14 ± 0.79 b19 ± 0.43 a11.4 ± 0.93 c
CEC (meq/100g)38.3 ± 4.3 b32.5 ± 5.5 b36.2 ± 4.2 b39.5 ± 4.6 b61.1 ± 4.5 a38.1 ± 3.9 b
TN (%)0.870 ± 0.020.805 ± 0.020.802 ± 0.10.785 ± 0.030.802 ± 0.040.826 ± 0.01
C/N ratio14 ± 0.514 ± 0.715 ± 0.815 ± 0.916 ± 0.616 ± 1.0
CO (%)12.5 ± 0.5 ab11.2 ± 0.7 b12.3 ± 0.6 ab12 ± 1.0 b12.5 ± 0.5 ab13.1 ± 0.7 a
Data are shown as median ± standard deviation. Different letters in the same file indicate significant differences between mean values corresponding to different treatment groups (p < 0.05).
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MDPI and ACS Style

Rengifo-Mosquera, G.; Salas-Moreno, M.; Gutierréz-Palacios, H.; Palacios-Torres, Y.; Romaña-Palacios, A.; Marrugo-Negrete, J. Composting as a Sustainable Solution for the Management of Plant Biomass Contaminated with Hg and As from Puddles Generated by Small-Scale Gold Mining in the Municipality of Unión Panamericana, Colombian Pacific. Sustainability 2024, 16, 9940. https://doi.org/10.3390/su16229940

AMA Style

Rengifo-Mosquera G, Salas-Moreno M, Gutierréz-Palacios H, Palacios-Torres Y, Romaña-Palacios A, Marrugo-Negrete J. Composting as a Sustainable Solution for the Management of Plant Biomass Contaminated with Hg and As from Puddles Generated by Small-Scale Gold Mining in the Municipality of Unión Panamericana, Colombian Pacific. Sustainability. 2024; 16(22):9940. https://doi.org/10.3390/su16229940

Chicago/Turabian Style

Rengifo-Mosquera, Gysela, Manuel Salas-Moreno, Harry Gutierréz-Palacios, Yuber Palacios-Torres, Allien Romaña-Palacios, and José Marrugo-Negrete. 2024. "Composting as a Sustainable Solution for the Management of Plant Biomass Contaminated with Hg and As from Puddles Generated by Small-Scale Gold Mining in the Municipality of Unión Panamericana, Colombian Pacific" Sustainability 16, no. 22: 9940. https://doi.org/10.3390/su16229940

APA Style

Rengifo-Mosquera, G., Salas-Moreno, M., Gutierréz-Palacios, H., Palacios-Torres, Y., Romaña-Palacios, A., & Marrugo-Negrete, J. (2024). Composting as a Sustainable Solution for the Management of Plant Biomass Contaminated with Hg and As from Puddles Generated by Small-Scale Gold Mining in the Municipality of Unión Panamericana, Colombian Pacific. Sustainability, 16(22), 9940. https://doi.org/10.3390/su16229940

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