Occurrence, distribution and sources of organochlorine pesticides (OCPs) in surface sediments from the Lijiang River, a typical karst river of southwestern China

Effects of hydrogeochemical conditions on the distribution of pesticides in the karst river system

Karst aquifer systems are tended to be polluted compared to other types of aquifers because pollutants are able to enter aquifers through developed conduit systems. To identify the effects of hydrogeochemical conditions on the distribution of pesticides in a karst river system in Kaiyang, southwest China, a typical pollution mode combining intermittent infiltration with intrusion was constructed. Twelve aqueous samples were collected along the karst river, and a total of 24 pesticides were detected. The results showed that the pesticide ubiquity and the dominant organophosphate (40%) and organonitrogen pesticides (49%) were both observed. Based on the spatial distribution, the attenuation of pesticides was found in the underground conduit and surface river. The wastewater treatment plant and the rural dump were the two important point sources releasing pesticides. In addition, ten core pesticides were identified by clustering analysis and regional characteristics of three types of pesticides in Songnen Plain, North China Plain, and Southwest karst areas were also summarized. With correlation analysis between pesticides and environmental factors, the significant correlations of pesticides with ammonium ion and dissolved oxygen were found, which indicated that rapid developing urbanization and long-term agricultural practices could remarkably affect the spatial distribution of pesticides. The calculation of ecological risk quotients showed that organophosphate pesticides had the highest risk to invertebrate, followed by organonitrogen pesticides, and finally organochlorine pesticides. Invertebrates were the most vulnerable aquatic organisms. These findings fill a gap in the multiple pesticides' pollution in the karst areas of China. Graphical abstract.

Comprehensive ecological risk assessment for semi-arid basin based on conceptual model of risk response and improved TOPSIS model-a case study of Wei River Basin, China

Comprehensive ecological risk assessment is of great significance for the restoration of watershed ecosystem health, and the appropriate and effective assessment method is the premise of ecological risk assessment. In this study, the conceptual model of risk response was developed by identification of ecological risk sources, stressors, endpoints and the corresponding response mechanism as well as the improved TOPSIS model based on Canberra distance and the combinatorial weighting method based on AHP and Critic were combined for the assessment. According to the three aspects of agriculture, industrial and urbanization, the occurrence mechanism of comprehensive ecological risk of rivers in semi-arid areas was analyzed. Furthermore, twenty-four indexes were selected to establish the index system and the Wei River Basin was taken as an example to verify the model. The results of comprehensive ecological risk assessment and stressor analysis showed that the deterioration of water quality (enrichment of heavy metals) and the decrease of benthos integrity were the two main risk factors for the increase of comprehensive ecological risk in Wei River Basin. And the regulation of ecological risk for the Wei River Basin is improvement of water quality and biotic integrity.

Pesticides in the typical agricultural groundwater in Songnen plain, northeast China: occurrence, spatial distribution and health risks

Songnen plain is an important commodity grain base of China, and this is the first study on the comprehensive detection of multiple pesticides in groundwater. Based on an analytical method of 56 pesticides, 30 groundwater samples were collected and analyzed. At least 4 pesticides were detected in each sample and 32 out of 56 pesticides were detected. The average detected levels of individual pesticides were approximately 10-100 ng/L. Organophosphorus pesticides and carbamate pesticides were the dominant pesticides, and their percentage of total pesticide concentrations were 35.9% and 55.5%, respectively. Based on the spatial distribution, the characteristic of nonpoint source pollution was indicated in the whole study area except for a point source pollution with the influence of a sewage oxidation pond. Nine core pesticides and three distinct clusters of the core pesticides with various concentration patterns were revealed by cluster analysis. Linear regression identified a significant relationship between the cumulative detections and the cumulative concentrations, providing access to identify the outlying contaminant events that deviate substantially from the linear trend. A new insight for prediction of pesticide occurrence was provided by the Pearson correlation between some individual pesticide concentrations and the cumulative detections or the cumulative concentrations. According to health risk assessment, the residual pesticides posed medium risks for children and infants and approximately 90% of risks were composed of β-HCH, dimethoate, ethyl-p-nitrophenyl phenylphosphonothioate and methyl parathion. These findings contributed to establishing a database for future monitoring and control of pesticides in agricultural areas.

Risk assessment of an organochlorine pesticide mixture in the surface waters of Qingshitan Reservoir in Southwest China

Risk assessment of single pollutants has been extensively studied. However, the co-exposure of pollutants in a real environment may pose a greater risk than single chemicals. In this study, concentration addition-based risk quotients were applied to the risk assessment of the 15 organochlorine pesticides (OCPs) mixtures (α-hexachlorocyclohexane (HCH), β-HCH, γ-HCH, δ-HCH, heptachlor, aldrin, heptachlor epoxide, chlordane, α-endosulfan, p,p′-dichloro-diphenyl-dichloroethylene, endrin, β-endosulfan, p,p′-dichloro-diphenyl-dichloroethane, p,p′-dichloro-diphenyl-trichloroethane, and methoxychlor) detected in the surface water (reservoirs, ponds, and streams) of Qingshitan Reservoir in Southwest China from 2014 to 2016 by summing up the toxic units (RQ_STU) of the toxicity data from the individual chemicals. The RQ_STU of the OCPs mixture exceeded 1 in 45.23% of the 283 surface water samples based on acute data and an assessment factor of 100, indicating a potential risk for the aquatic environment (fish). Methoxychlor and γ-HCH contributed the most toxicities in the pesticide mixtures toward Daphnia and fish and provided at least 50% of the mixture toxicity in all samples with RQ_STU larger than 1. The most sensitive organism to realistic OCPs mixtures in the surface waters of Qingshitan Reservoir was fish, followed by Daphnia and algae. The values of the maximum cumulative ratio for all samples indicated that the risk assessment based on single chemicals underestimated the pesticide mixture toxicities, which shows that special consideration should be made for the ecological risk of pesticide mixtures in the aquatic environment.

Risk assessment of single pollutants has been extensively studied.

Depth-distribution, possible sources, and toxic risk assessment of organochlorine pesticides (OCPs) in different river sediment cores affected by urbanization and reclamation in a Chinese delta

Sediment cores were collected in urban (0-50 cm), rural (0-40 cm) and reclamation-affected river (0-40 cm) environments in the Pearl River Delta. Concentrations of 16 organochlorine pesticides (OCPs) were determined in all collected samples to identify the depth-distribution, possible sources and ecotoxicological risks of OCPs in river sediments affected by urbanization and reclamation in a Chinese delta. The results showed that the top 10 cm of rural river sediments had slightly lower concentrations of the 16 OCPs compared to urban and reclamation-affected rivers, whereas the 30-40 cm sediment layers in the rural river showed higher levels of the 16 OCPs. However, higher OCPs levels were observed in the 20-30 cm sediment layers in the urban river than in the rural and reclamation-affected rivers. The principal OCPs in most deeper sediment layers were hexachlorobezene (HCB), the combination of aldrin, endrin and dieldrin (ΣDRINs) and the combination of α-HCH, β-HCH and γ-HCH (ΣHCHs). The predominant OCPs in surface sediments were HCB, ΣDRINs and the combination of p,p'-DDD, o,p'-DDT, p,p'-DDT and p,p'-DDE (ΣDDTs). Generally, OCP concentrations decreased with depth along sediment profiles at most sampling sites in the three types of rivers. The source analyses indicated that some sampling sites were still suffering from the recent use of hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs) and aldrin. According to the soil quality thresholds of China, the levels of HCHs and DDTs at most sampling sites were below class Ⅰ criteria. Based on the sediment quality guideline quotient (SQGQ), the combined ecotoxicological risk of OCPs (γ-HCH, dieldrin, p,p'-DDD, p,p'-DDE and p,p'-DDT) in surface sediments (0-10 cm) was higher than deeper sediments, and the rural river sediments exhibited a higher combined ecotoxicological risk than the sediments in urban and reclamation-affected rivers.