Human Health Risk Assessment of Phenolic Contaminants in Lake Xingkai, China

Abstract

Cresols are aromatic organic compounds widely used in industrial and agricultural production. They have been detected in large quantities in aquatic environments, posing health risks such as skin irritation, gastrointestinal stimulation, and chronic neurological effects. In this study, we investigated the exposure concentration of cresols in the water bodies of Lake Xingkai (i.e., Daxingkai and Xiaoxingkai Lakes) during four typical hydrological periods (30 April, 22 June, 5 September, and 1 November 2021), assessed the human health risk from phenolic contaminants using the mean value method, and determined the health risk of adult cresol exposure in the Lake Xingkai watershed based on local population exposure parameters. This study developed a water environmental pollution health risk assessment model based on the methodology proposed by the United States Environmental Protection Agency (US EPA). It further evaluated the health risks to humans posed by phenolic pollutants via the drinking water pathway. The results revealed that the concentration range of cresols in water bodies was between 5.91 × 10⁻¹ ng·mL⁻¹ and 6.68 ng·mL⁻¹. The adult drinking water health risk values of cresols in the Lake Xingkai watershed were between 3.15 × 10⁻⁴ and 3.57 × 10⁻³, and all water samples from the 10 sites had hazard quotient (HQ) values less than 1, indicating that the non-carcinogen risk was small or negligible. The cresol HQ value in the water of Xiaoxingkai Lake was 4.6 times that found in Daxingkai Lake.

1. Introduction

Phenolic compounds arising from the substitution of hydrogen atoms with hydroxyl groups on the benzene rings of aromatic hydrocarbons are widely used as herbicides, pesticides, fungicides, and wood preservatives [1,2]. They are key constituents of effluents produced by the paper manufacturing industry [3]. Upon entering the environment, these compounds undergo a succession of physicochemical processes, including volatilization, adsorption–desorption, hydrolysis, natural sunlight-mediated photodegradation, biodegradation, and biomagnification, leading to their transformation and migration [4,5]. The phenolic hydroxyl groups (-OH) enhance lipophilicity and reactivity, enabling phenolic compounds to disrupt metabolic processes in organisms. Halogenated phenols are highly persistent and bioaccumulative, posing serious health risks. When released into Xingkai Lake, polycyclic and halogenated phenols resist degradation and remain in the environment for prolonged periods. Phenolic compounds with high octanol-water (Kow) partition coefficients are readily adsorbed by sediments and aquatic organisms, thus increasing the likelihood of human exposure via the food chain. Furthermore, when phenolic compounds coexist with other pollutants, they may undergo complexation reactions, amplifying synergistic toxicity [6,7]. For instance, when phenolic substances combine with iron, they will, under the action of the Fenton reaction, promote the generation of hydroxyl radicals, thereby causing combined toxicity to living organisms [8]. Given the limited water mobility in Xingkai Lake, the risk of phenolic compound accumulation is exacerbated. Therefore, from a chemical perspective, the investigation of phenolic pollutants in Xingkai Lake holds substantial significance. Phenolic compounds persist in the natural environment for extended periods and may exist in one or more forms. In particular, the contamination of surface water bodies with phenolic compounds poses direct threats to human health and indirect dangers via the food chain. These compounds can penetrate the body through the skin, mucous membranes, respiratory system, and digestive tract, leading to protein denaturation and subsequent precipitation, potentially causing cellular mutations that may eventually lead to cancer [9,10,11]. Therefore, monitoring the concentrations of phenolic contaminants in drinking water and assessing their corresponding risks to human health are of critical importance.

In recent years, domestic scholars have begun examining the human health risks posed by phenolic compounds in surface waters. For example, Wang et al. (2012) investigated the spatial distribution characteristics of phenolic contaminants in the Songhua River and found that the concentration of phenolic contaminants in the mid-to-low reaches of the river was higher than that in the upstream region, with the highest total phenol concentration values observed at the monitoring sections of Jiamusi downstream, Mudanjiang upstream, and Dadingzishan in the midstream section of the river [12]. Xu et al. (2021) studied the phenolic pollution in Poyang Lake and corresponding health risks [13] and reported that the concentration range of phenol was ND–556.26 ng·L⁻¹ and the health risk via drinking water pathways was from 3.80 × 10⁻⁷ to 8.46 × 10⁻⁵. These studies have largely focused on water bodies in southern China; however, attention paid to the lakes, particularly international boundary lakes, in the cold and dry regions of northeast China has been relatively scarce. Similar to other lakes, Lake Xingkai receives and stores large amounts of contaminants from Chinese terrestrial sources, connecting upstream and downstream landscape changes and playing an ecological role as a lake in terms of drinking water and aquatic produce. However, owing to its unique geographical location and the differences in policies for the joint management of international boundary lakes, Lake Xingkai is facing a serious threat of environmental pollution, culminating in a significant challenge due to ecological resources and cross-border environmental disputes.

Lake Xingkai serves as the source of the Ussuri River and is the primary water supply for several cities in Jixi City and Mishan City in Heilongjiang Province [14]. Since the 1950s, intensive agricultural development around lakes has led to serious agricultural non-point source pollution and reduced wetland areas [15]. The “2022 Environmental Status Report of Heilongjiang Province” stated that Daxingkai and Xiaoxingkai Lakes fall under Classes V and IV of water bodies, respectively, according to the “Standards for Surface Water Environmental Quality” GB 3838-2002 [16], exhibiting a low level of eutrophication. The primary factors exceeding the standards were total phosphorus, total nitrogen, and the manganese dioxide index. Daxingkai Lake has a Class V water quality classification, indicating moderate pollution with a low level of eutrophication. Compared with 2021, no significant changes in water quality or nutrient status have been noted. Xiaoxingkai Lake has a Class IV water quality classification, indicating slight pollution and a low level of eutrophication. Compared with 2021, no notable changes in water quality or nutrient status have occurred here either. The deterioration of the water quality in Lake Xingkai is closely related to the rapid development of industries and agriculture within the watershed, and particularly to the excessive use of fertilizers [15,17]. Therefore, research on the phenolic contaminants and water quality of Lake Xingkai is essential to comprehensively understand the changes in the aquatic environment of the lake.

Human health risk assessments for aquatic environments primarily focus on substances that are harmful to humans in water bodies. These substances can be divided into two categories: genotoxic and somatic. Genotoxic substances include radioactive contaminants and chemical carcinogens, whereas somatic toxicants refer to non-carcinogens. Based on the classification system developed by the International Agency for Research on Cancer through comprehensive evaluations of the reliability of carcinogenicity for chemical toxicants, as well as research on the adverse effects of harmful substances on human health through the drinking water pathway, a risk model for health hazards caused by carcinogens and non-carcinogens can be established [18,19,20]. In this study, we assessed the human health risks posed by the phenolic contaminants in Lake Xingkai by measuring their concentrations. Using the health risk assessment model recommended by the United States Environmental Protection Agency (US EPA), we provided a preliminary evaluation of the health risks associated with phenolic contaminants in lake water through the drinking water pathway. This study fills a research gap by assessing the quality and safety of water affected by phenolic pollution in Lake Xingkai, tracing the sources of phenolic pollution, and understanding the migration and transformation of contaminants. It also provides scientific evidence for formulating environmental protection strategies for international boundary lakes and can serve as a reference and guidance for protecting and restoring the ecological health of lake areas.

2. Materials and Methods

2.1. Research Area

Lake Xingkai (43°55′–46°30′ N, 131°25′–134°20′ E) is located in the southern part of the Sanjiang Plain in Northeast China (Figure 1). It is a graben-type tectonic depression lake and the largest freshwater lake in East Asia. The watershed is formed by the joint actions of the Muling River, Lake Xingkai, and Ussuri River, with a drainage basin area of 3.64 × 10⁴ km². The average annual inflow volume is approximately 55.68 × 10⁸ m³, and the average water depth is 1.8 m. The lake experiences annual precipitation of 530–600 mm and an average annual evaporation of 636–755 mm. Lake Xingkai also undergoes an annual freezing period from November to March, during which the thickness of the ice layer ranges from 0.8 to 1.5 m. The flood season occurs between July and September. The lake area is perennially dominated by westerly winds, with an average wind speed of 3.3 m·s⁻¹. Lake Xingkai comprises two lakes, large and small, connected by a natural sandbar. Daxingkai Lake covers an area of 4190 km², with 1160 km² of its northern waters belonging to China. Additionally, because of the shallow, saucer-shaped bottom of Daxingkai Lake, the surface is often subjected to large waves and currents, resulting in an unstable, muddy lake bed. This leads to the frequent suspension of sediments, resulting in turbid coastal waters [21].

2.2. Sample Collection

The sampling sites were strategically positioned based on geographical constraints, geopolitical boundaries, and environmental monitoring principles. For Xiaoxingkai Lake—entirely within China’s territory, and with a smaller surface area—four equidistant sampling sites were deployed horizontally along its latitudinal central zone to avoid shoreline pollution interference while covering the main water body. For the Chinese sector of transboundary Daxingkai Lake (characterized by a northwestern zonal distribution and larger surface area), six equidistant sites were arranged east–west along its north–south central axis. This design minimized boundary-related operational constraints and shoreline pollution impacts, ensuring representative coverage of China’s jurisdictional waters. The spatial configuration guarantees that monitored pollution levels reflect regional aquatic environmental conditions.

Water samples were collected from ten representative locations in Lake Xingkai during four typical hydrological periods (30 April, 22 June, 5 September, and 1 November 2021). At each location, three surface water subsamples (0–50 cm depth) were obtained using a stainless steel sampling bucket and composited to form a single integrated sample. Two liters of the integrated sample were transferred into 1 L brown glass bottles (Changchun Kailun Scientific Instrument Co., Ltd., Changchun, China), acidified to pH 2–3 with 6 mol·L⁻¹ hydrochloric acid (Changchun Kailun Scientific Instrument Co., Ltd., Changchun, China) to suppress microbial activity, and preserved at 0–4 °C during transport under dark conditions.

A total of 40 integrated samples were acquired (10 locations × 4 sampling campaigns). For quality control, two duplicate samples were additionally collected per sampling campaign, yielding eight quality control samples. Thus, 48 water samples were ultimately obtained.

Upon arrival at the laboratory, all samples were filtered through 0.45 μm glass fiber filters (Changchun Huayu Glass Instrument Co., Ltd., Changchun, China) and refrigerated at 4 °C. Phenolic contaminants and routine water quality parameters (such as chlorophyll-a and suspended solids concentration) were analyzed within 72 h of collection.

2.3. Reagents and Instruments

Chemical Reagents

Dichloromethane (CH₂Cl₂; Sinopharm Chemical Reagent Co. Ltd., Shanghai, China): chromatography grade; propanol pentafluorobenzyl bromide dibromomethane. As a liquid–liquid extraction (LLE) solvent, dichloromethane enables the partitioning of phenolic and other organic analytes from aqueous matrices, facilitating downstream analytical processing via its high organic-solute solubility and immiscibility with water.

2.4. Determination of Phenols in Water Bodies

2.4.1. Sample Pretreatment

The water sample (200 mL) was transferred into a 500 mL separatory funnel (Changchun Kailun Scientific Instrument Co., Ltd., Changchun, China) and extracted twice with 20 mL of dichloromethane (Sinopharm Chemical Reagent Co. Ltd., Shanghai, China). The organic phases were combined under reduced pressure until nearly dry, and the concentrated sample was then replaced with acetone until nearly dry. The concentrating flask was washed twice with 5 mL of acetone (Sinopharm Chemical Reagent Co. Ltd., Shanghai, China), the washings were combined in a 15 mL reaction flask (Changchun Kailun Scientific Instrument Co., Ltd., Changchun, China), and 100 µL of derivatization reagent (Sinopharm Chemical Reagent Co. Ltd., Shanghai, China) was added to the flask. (Pentafluorobenzyl bromide: this derivatization reagent undergoes nucleophilic substitution with phenolic moieties to generate volatile pentafluorobenzyl esters, enhancing chromatographic resolution and detection sensitivity for gas chromatography–mass spectrometry (GC-MS) analysis; 5% acetone solution: employed for solvent exchange during the evaporation/concentration step, where acetone replaces dichloromethane to facilitate subsequent derivatization. It also serves as the carrier solvent for formulating derivatization reagent and internal standard (IS) solutions.) The mixture was derivatized at 60 °C for 1 h, cooled, added to an internal standard, and mixed well before injecting the sample for analysis [22]. (Dibromomethane: as an internal standard, dibromomethane normalizes for instrumental variability and injection errors during quantitative analysis, enabling the precise quantification of target analytes through response factor calibration; 100 µg·mL⁻¹ acetone solution.)

2.4.2. Instrumental Conditions

Gas chromatography/tandem mass spectrometer (TRACE1310/TSQ8000evo; Shimadzu Corporation, Kyoto, Japan) was used to determine the cresol content. The following are the conditions set for the analysis: analytical chromatography column, DB-5, 30 m × 0.25 mm × 0.25 µm; column temperature, 50 °C (2 min) 10 °C/min–250 °C (5 min); carrier gas, high-purity helium, 1.0 mL·min⁻¹; vaporization temperature, 250 °C; ionization source, EI, 70 eV.

2.4.3. Quality Control

Each batch of samples was analyzed once for the middle concentration point of the standard curve, and the measured result had a relative deviation ≤ 20% compared to the initial curve’s measured concentration at that point. During the sample testing process, a spiked recovery experiment was performed, and the results indicated that the spiked recovery rates ranged from 91% to 108%. In this study, the concentrations of o-cresol, m-cresol, and p-cresol in the water were quantitatively determined individually. Subsequently, the detection results for these three components were aggregated to calculate the total cresol content data. Information on the ion pairs used for multiple reaction monitoring is presented in

Table 1. Information on ion pairs for multiple reaction monitoring.

Name	RT	Ion Polarity	Window	Pre-Width	Post-Width	Mass	Product Mass	Collision Energy
Internal Standard	12.3	Positive	1	0	0	250	169	10
Surrogate	14.14	Positive	1	0	0	292	181	15
Cresol	15.2	Positive	1	0	0	288	181	10

. Based on the measured data, a standard curve for phenolic contaminants was created, as seen in Figure 2.

2.5. Determination of Water Quality Parameters

The concentration of total suspended matter (TSM) was determined using the weight method, wherein Whatman filters (Changchun Huayu Glass Instrument Co., Ltd., Changchun, China) with a pore size of 0.45 μm were first dried at 103–105 °C for 4 h to remove organic matter. The filters were weighed after cooling. Following the passage of a specific volume of water sample through the filter, the filter was transferred into an oven set at 103–105 °C and dried for an additional 4 h, after which it was weighed again. Finally, TSM concentration was calculated using the weight method. The concentration of chlorophyll-a (Chl-a) was determined using a standard spectrophotometric method. After filtering a specific volume of the water sample using a fiber membrane, the sample was extracted with 90% acetone. Following centrifugation at 3000× g r·min⁻¹ for 20 min, the supernatant was collected and the absorbance was measured using a Shimadzu UV-2600 PC spectrophotometer (Kyoto, Japan). The Chl-a concentration was calculated based on the volume. Turbidity was measured using a photometric method.

2.6. Methodology for Human Risk Assessment

This study employed the quotient method for the human health risk assessment of cresols, focusing on both carcinogenic and noncarcinogenic risk evaluations. Given that cresols are categorized as a Group 3 carcinogen by the International Agency for Research on Cancer, some controversy regarding their carcinogenicity persists. Current research findings do not fully determine the carcinogenic risk of cresols in humans. Therefore, this study evaluated only the cresol-associated noncarcinogenic risks to human health. The noncarcinogenic risk assessment was based on the US EPA-recommended risk assessment method [23,24], using the ratio of the exposure dose of the pollutant at a specific time to the reference dose of the pollutant via the exposure pathway to assess the health risk to humans using the threshold value hazard quotient (HQ) for noncarcinogens. Equation (1) was used to calculate the HQ [13]. In the context of human health risk assessments, the US EPA recommends a noncarcinogenic risk threshold of 1. If HQ is greater than 1, there is a noncarcinogenic risk [25]; if HQ is less than 1, the noncarcinogenic risk is considered small or negligible [26].

$$\mathrm{H}\mathrm{Q}={\displaystyle \frac{\mathrm{A}\mathrm{D}\mathrm{D}}{\mathrm{R}\mathrm{f}\mathrm{D}}}$$

(1)

In Equation (1), HQ denotes the noncarcinogenic risk threshold; ADD stands for the daily average exposure dose of the pollutant, mg·(kg·d)⁻¹; and RfD refers to the reference dose of the pollutant for average daily drinking water intake, in mg·(kg·d)⁻¹.

By monitoring the concentration of contaminants in the environmental media to which humans are exposed and estimating the exposure doses of different populations in different environmental media using Equation (2), the daily average exposure (ADD) dose of cresols via drinking water intake was computed [27,28].

$$\mathrm{A}\mathrm{D}\mathrm{D}={\displaystyle \frac{\mathrm{c}\times \mathrm{I}\mathrm{R}\times \mathrm{E}\mathrm{F}\times \mathrm{E}\mathrm{D}}{\mathrm{B}\mathrm{W}\times \mathrm{A}\mathrm{T}}}$$

(2)

In Equation (2), c represents the concentration of cresols in water bodies, mg·mL⁻¹; IR denotes the average daily drinking water intake, mL·d⁻¹; EF stands for the exposure frequency, d·a⁻¹; ED refers to the exposure duration, a; BW indicates the average human body weight, kg; and AT denotes the average exposure duration, d.

In this study, RfD for phenolic contaminants was set at 5·10⁻² mg·(kg·d)⁻¹, EF was 365 d·a⁻¹, ED was 70 a, and AT was 25,550 d. The cresol concentration detected in each batch of water samples was substituted into Equation (2) for the calculations.

2.7. Statistical Analysis

SPSS software (version 17.0) was used for Pearson correlation analysis, calculating the correlation coefficient r and conducting a double-tailed significance test (two-tailed), where * indicates p < 0.05 and ** indicates p < 0.01. Variance analysis was performed to analyze the differences in the concentrations of cresol phenolic contaminants between the Daxingkai and Xiaoxingkai Lakes. Using Origin 2021 software, we generated a Correlation Heatmap demonstrating the levels of contaminants and water quality parameters across various sampling locations.

3. Results and Discussion

3.1. Distribution Characteristics, Sources, and Results of the Water Quality Parameter Determination Analysis of Phenolic Contaminants in the Water Column of Lake Xingkai

Extensive farms and fields surround Xiaoxingkai Lake [29]. The use of phenolic pesticides and fertilizers has led to large amounts of phenolic contaminants entering lake water through rain or irrigation, causing pollution [30,31]. Animal feces and urine from farms may contain phenolic compounds, which can lead to an excess of phenolic contaminants when discharged into the lake water. In addition, paper mills and limestone powder plants are located upstream of and around Xiaoxingkai Lake. These industries generate large amounts of phenolic contaminants during their production processes, and phenol and its derivatives are also present in industrial wastewater. For instance, phenol and its derivatives are extensively utilized in various chemical engineering sectors, such as petrochemicals, plastics, pesticides, dyes, phenolic resins, epoxy resins, and polyamide resins [32]. The primary sources of pollution in Xingkai Lake are attributed to the inflow of contaminated river water (point source pollution) and extensive farmlands surrounding the lake (non-point source pollution). Xingkai Lake serves as the receiving water body for several rivers, including the Muling River and Songachao River. The river water entering Xingkai Lake is significantly polluted by industries such as coal mining, paper production, and mineral extraction [15,17]. Additionally, the extensive use of pesticides in farmlands around Xingkai Lake results in pesticide residues accumulating in the soil. During periods of surface runoff, these residual pesticides from farmlands adjacent to the lake are transported into Xingkai Lake (various pesticides have been detected) [33,34,35,36]. Consequently, Xingkai Lake acts as the ultimate recipient of pollutants originating from its surrounding areas and the upstream river basin. Phenolic compounds detected in the lake water pose potential risks to human health via pathways such as the food chain and drinking water consumption [21]. The greater water storage capacity of Lake Daxingkai in comparison to Lake Xiaoxingkai provides it with enhanced self-purification capability. This facilitates the effective dilution of phenolic contaminants entering the water body and allows sufficient time for their degradation. Consequently, the concentrations of phenolic contaminants in the Lake Daxingkai area were significantly lower than those observed in the Lake Xiaoxingkai area.

In addition to the primary sources of the aforementioned phenolic pollutants, secondary sources also exist. In Xingkai Lake, Pseudomonas bacteria convert phenol to cresol through methylation catalyzed by methyltransferase. The catalytic efficiency of this biotransformation process peaks under high-temperature conditions in summer [37]. Chlorophenol pesticide input is also a minor source of cresol. The partial thermal cracking of phenolic compounds in pesticides releases cresol as a degradation by-product, thereby adding to the pollution of this lake ecosystem [38].

The concentrations of water quality parameters in the water column of Lake Xingkai are illustrated in Figure 3. Both Daxingkai and Xiaoxingkai Lakes exhibited an initial increase, followed by a decrease in water quality parameters, peaking in June and showing significant differences between the months. The highest levels of turbidity, TSM concentration, and Chl-a content were observed in June, with values of 85.30 NTU, 81.96 ng·mL⁻¹, and 1.61 ng·mL⁻¹ for Daxingkai Lake, and 78.18 NTU, 45.03 ng·mL⁻¹, and 5.92 ng·mL⁻¹ for Xiaoxingkai Lake, respectively. This is because June is the rainy season, which results in significant increases in runoff inflow, rainfall, and substantial disturbances in the water column of Lake Xingkai. Moreover, ample sunlight and rising temperatures facilitate algal growth and reproduction, leading to elevated water column turbidity, TSM concentration, and Chl-a content. September and April had the next highest values, whereas November exhibited the lowest values of water column turbidity, TSM concentration, and Chl-a content. For Daxingkai Lake, the values were 24.97 NTU, 36.59 ng·mL⁻¹, and 0.56 ng·mL⁻¹, respectively, and, for Xiaoxingkai Lake, they were 19.33 NTU, 16.28 ng·mL⁻¹, and 1.73 ng·mL⁻¹, respectively.

The water column turbidity and TSM concentration in Daxingkai Lake were significantly higher than those in Xiaoxingkai Lake, whereas the Chl-a content was just the opposite, with Daxingkai Lake having significantly lower Chl-a than Xiaoxingkai Lake. The higher turbidity and TSM concentrations in Daxingkai Lake were related to its larger size and more complex hydrodynamic conditions, such as stronger wind waves and currents, which enabled the particles to be suspended in water, making the water more turbid. Xiaoxingkai Lake was affected by runoff from northern farmlands and pastures, leading to a higher nutrient status and more vigorous algal growth, resulting in higher Chl-a content [39].

As shown in Figure 3, the concentration of cresols was low in April during the ice-covered period in Lake Xingkai; peaked in June, followed by September; and was the lowest in November. Concentration of cresols in the water column of Daxingkai Lake ranged from 2.10 × 10⁻¹ to 1.10 ng·mL⁻¹, with an average of 0.51 ng·mL⁻¹, whereas in Xiaoxingkai Lake, that concentration ranged between 1.13 and 4.37 ng·mL⁻¹, with an average of 3.43 ng·mL⁻¹.

3.2. Correlation Analysis Between Cresols and Water Quality Parameters

The results of the correlation analysis between cresols and water quality parameters revealed that cresols exhibited a significant negative correlation with TSM concentration (r = −0.68; p < 0.05; Figure 4), whereas the negative correlation with water column turbidity did not reach a significant level (r = −0.52; p > 0.05). However, cresols showed a moderately positive correlation with Chl-a content (r = 0.55; p > 0.05). Additionally, water column turbidity and TSM concentration demonstrated a highly significant positive correlation (r = 0.97; p < 0.01), whereas Chl-a content was significantly negatively correlated with TSM concentration (r = −0.73; p < 0.05).

Organic contaminants (phenols) entering water bodies may form suspended solids or colloids under certain environmental conditions, thereby increasing water turbidity [40]. Additionally, some organic contaminants may continue to bind with suspended solids in water, further exacerbating turbidity and TSM concentration. When there are many suspended solids in a water body, the light penetration ability decreases, inhibiting algal photosynthesis, leading to reduced chlorophyll content. Therefore, an increase in water turbidity under certain environmental conditions reduces chlorophyll content. Thus, when organic contaminants (phenols) are discharged into a water body, the combined effects of various environmental conditions lead to an increase in water turbidity and TSM concentration and a further reduction in chlorophyll content [41,42]. The peak concentration of phenolic contaminants in Lake Xingkai during June is primarily driven by intensified agricultural non-point source pollution coupled with enhanced rainfall-runoff transport. This critical period coincides with (i) the early summer peak in farming activities, involving the extensive application of phenol-containing agrochemicals (e.g., pentachlorophenol pesticides and nitrophenolic fertilizers), and (ii) the onset of the regional wet season, characterized by frequent high-intensity precipitation events. These synergistic drivers mediate substantial leaching of residual phenolics from agricultural soils into lacustrine systems through surface runoff and drainage networks, triggering significantly elevated aqueous-phase concentrations basin-wide during summer months. Consequently, as graphically demonstrated, summer exhibits the annual maximum in phenolic contaminant levels across the hydrological cycle.

3.3. Risk Assessment of the Impact of Phenolic Contaminants on Human Health

The characteristics of population exposure behaviors in the environment are key factors determining the accuracy of environmental health risk assessments. When the concentration of pollutants in environmental media is accurately quantified, the selection of exposure parameter values becomes closer to the actual exposure situation of the target population, making the evaluation result of the exposure dose and the result of the environmental health risk assessment more accurate [43]. There are differences in population exposure parameters in different areas. The health risks of cresols were evaluated based on the exposure parameters of the population in Lake Xingkai Basin and the detection of phenolic contaminants in lake water. The drinking water intake rate (IR) for the population in the Lake Xingkai Basin was taken as 2000 mL·d⁻¹, and the average BW was 75 kg. The HQ values for the health risks posed by cresols in drinking water from various monitoring points in Lake Xingkai are presented in Figure 5.

The noncarcinogenic health risk of cresols via drinking water in Lake Xingkai was determined to be between 3.15 × 10⁻⁴ and 3.57 × 10⁻³, with the highest HQ value of 3.57 × 10⁻³ and the lowest of 3.15 × 10⁻⁴. The difference between the highest and lowest values was one order of magnitude, but all HQ values obtained from the 10 sampling points were less than 1, indicating that the noncarcinogenic health risk of cresols in Lake Xingkai was minimal and could be ignored. The HQ values for cresols detected in water samples collected from various sampling points in Daxingkai Lake were all less than 1.0 × 10⁻³, whereas those in Xiaoxingkai Lake were all greater than 1.0 × 10⁻³. The HQ value for cresols in Xiaoxingkai Lake was 4.6 times higher than that in Daxingkai Lake, indicating that the health risk of cresols in the water body of Xiaoxingkai Lake was relatively higher compared to that of Daxingkai Lake.

4. Conclusions

This study examined the exposure concentration of cresols in Lake Xingkai through water sample analysis conducted in April, June, September, and November of 2021. This study evaluated the human health risk of cresols and determined the health risk of adult cresol exposure in the Lake Xingkai watershed area based on local population exposure parameters. Sample collection for this study was conducted on four occasions: 30 April, 22 June, 5 September, and 1 November 2021. We conclude the following:

(1)

The concentration range of cresols in the water column of Lake Xingkai was between 5.91 × 10⁻¹ and 6.68 ng·mL⁻¹. The concentration of cresols in the water of Xiaoxingkai Lake was generally higher than that in Daxingkai Lake.

(2)

The health risk of drinking water in the Lake Xingkai Basin was between 3.15 × 10⁻⁴ and 3.57 × 10⁻³, whereas the non-cancer risks in the Daxingkai and Xiaoxingkai Lakes were at acceptable levels. The non-cancer risk coefficient for cresols in Xiaoxingkai Lake was one order of magnitude higher than that in Daxingkai Lake, indicating that the human health risk of cresols from Xiaoxingkai Lake should be monitored and managed more closely and that water treatment measures should be implemented to ensure the safety of drinking water.