Pesticide Residues in Urban and Semi-Urban Regions of West Bengal, India: Risk Assessment in Human Milk and Water

Anand, Niharika (2019) Pesticide Residues in Urban and Semi-Urban Regions of West Bengal, India: Risk Assessment in Human Milk and Water. PhD thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Older and more persistent classes of pesticides, such as the organochlorines, are gradually being replaced across the world by relatively newer compounds, such as the pyrethroids and the neonicotinoids. Understanding and managing this transition requires targeted regulation. This is facilitated by knowledge of the contamination status as well as the environmental and socio-economic factors that shape human exposure to these chemicals. This study investigates the occurrence and distribution of the organochlorines as well as the emerging pyrethroids and neonicotinoids in human milk and water in West Bengal, India. While agricultural regions (semi-urban and rural) were historically more at risk of exposure, recent reports indicate that urban areas, with higher pesticide application for public health, may now be at greater risk. If this trend extends across developing nations with similar trajectories of pesticide use, regulations require appropriate modification. However, to establish this trend, further investigation is needed in other regions and populations. This study compares the contamination status between a semi-urban location with both agricultural and built-up areas (Nadia) and an urban one (Kolkata) in West Bengal, India. The indicator of choice is the concentration in human milk, which is a sensitive measure of the general exposure of a population. Regulated by the Stockholm Convention on Persistent Organic Pollutants, India has banned the use of organochlorines such as DDT in agriculture but continues restricted use for disease control. Despite these regulations, the concentrations of these chemicals are reported to have increased in human milk in recent decades in the city of Chennai, India. This study investigates the impact and extent of this trend by examining the temporal variation of pesticide concentration in human milk in the urban region of Kolkata, India. This knowledge will enable further targeted regulation of pesticides in the country. This, in turn, will reduce the worldwide contamination that occurs through atmospheric long-range transport. Our results may serve as a model of the contamination status of developing countries and enable better regulation in these nations as well. We calculated the Estimated Daily Intake (EDI) of breastfeeding infants and compared with the Tolerable Daily Intake (TDI). We also investigate the pesticide concentrations in the surface water and groundwater of the semi-urban region and associated hazardous effects to the non-target aquatic organisms. While multiple studies have reported organochlorines in human milk and water in various regions of India, there exists little information on neonicotinoids and pyrethroids. To the best of our knowledge, the investigation of pyrethroids in human milk in India has been carried out till date in the Punjab region alone. Also to the best of our knowledge, the investigation of neonicotinoid concentrations in human milk is yet to be carried out. This is the first systematic and comprehensive study to report the status of organochlorines, pyrethroids and neonicotinoids in human milk and water in the semi-urban region of Nadia, West Bengal. Organochlorines have been used extensively for long periods across the world in order to control agricultural pests and vector borne diseases such as malaria, kala-azar and dengue. Pyrethroids are among the most frequently used pesticides and are widely used in agricultural and urban areas, primarily for structural pest control and as pet sprays and shampoos. Neonicotinoids are insecticides with novel modes of action and are used extensively in agriculture. This study describes a single extraction procedure for the simultaneous analysis of organochlorines, neonicotinoids and pyrethroids in human milk. A simple, rapid, operator friendly as well as economic procedure has been developed and validated. This is a modification of the existing QuEChERS method. To the best of our knowledge, this is the first validated method to detect neonicotinoids in human milk. We optimized the extraction of the chemicals from whole milk and report our solutions to the problems of interference by co-extracted substances. The clean-up method was optimized using a minimum amount of PSA (50 mg) and MgSO₄ (150 mg). This was followed by GC-MS/MS analysis (for organochlorines and pyrethroids) and LC-MS/MS (for neonicotinoids). The method was validated following SANTE/11945/2015 guidelines at concentrations 10, 20 and 100 ng g⁻¹. Limits of quantification (LOQ) were obtained at ≤ 2 ng g⁻¹ for all pesticides and lowest validated level (LVL) were 10 ng g⁻¹, with measurement uncertainty between 0.47 and 2.6 ng g⁻¹. Average recovery ranged from 84 % to 102 % and was found to be more satisfactory than the original QuEChERS, AOAC 2007.01 acetate buffer method and the modified QuEChERS methods. The relative standard deviation was less than 16 %. The method was successfully applied for the analysis of human milk samples collected in West Bengal, India. This study investigates the variation in pesticide exposure in human milk between the urban region of Kolkata and the semi-urban area of Nadia, West Bengal. Despite the fact that most organochlorines are banned and restricted for use in India, residues of these compounds continue to be present in the environment. Of the organochlorines, the following pesticides were found in human milk in both urban and semi-urban regions: o,p′ DDD, p,p′ DDD, p,p′ DDT, β-HCH, γ-HCH, δ-HCH, α-endosulfan, β-endosulfan and aldrin. A number of organochlorines and pyrethroids and all tested neonicotinoids (imidacloprid, thiacloprid and acetamiprid) were ‘not detected’ in the samples. These results reveal that the concentration of pesticides in mothers’ milk, particularly DDTs and HCHs are ubiquitous in both regions. For the majority of the chemicals screened in this study (DDT and its metabolites, HCH isomers, bifenthrin and endosulfan), we found a distinct urban>suburban trend. The higher level of pesticide residues in the samples from the urban region implies region specific and local sources (such as chemical industries located in the area). Also, HCH and DDT levels have increased considerably in Kolkata compared with the data collected a decade before. DDT was detected in soil samples and surface water of Hooghly River flowing through the outskirts of Kolkata. Three pyrethroids were detected in human milk samples in India for the first time, indicating their potential for bioaccumulation and contradicting the assumption that pyrethroids are easily metabolized by hydrolysis in mammals. Daily intake estimation of nursing infants was calculated and compared with acceptable WHO/FAO levels. The Estimated Daily Intake of DDTs, HCHs, aldrin, dieldrin, β-endosulfan and bifenthrin exceeded the Tolerable Daily Intake (TDI), which is a major health concern for the infants in this region. The national and international comparison of pesticide concentration indicated that the residue levels of HCHs and DDTs observed in urban region was higher than the other studies reported from the Indian cities such as Delhi, Mumbai, Chennai and Punjab and developing nations such as Vietnam, Malaysia. Hence it is evident that mothers in this region are exposed to the pesticidal residues present in different environmental matrices and current levels might have resulted from the bioaccumulation of pesticides in the food chain. This study also investigates the contamination status of organochlorines, pyrethroids and neonicotinoids in surface water and groundwater of Nadia, West Bengal. The extensive use of organochlorines in the past, limited ongoing usage and persistence have resulted in the ubiquitous presence of these chemicals in the environment. The other organochlorines detected in the water samples are endosulfan and HCB. Atmospheric deposition, agricultural run-off and industrial activities along the bank of the river Ganga are potential sources of organochlorines in this region. The pyrethroids detected in the surface and groundwater of the region is permethrin and deltamethrin. The presence of these chemicals indicates an increase in the consumption pattern of pyrethroids. Our results indicate that seasonal variations significantly affect the concentrations of pesticide in water. An ecotoxicological risk assessment of exposure showed that the lower trophic level organisms were adversely affected by the prevalent concentrations of DDT, endosulfan and lindane in the surface waters. This also revealed that the fish species were largely affected by the endosulfan concentrations in this region, which cannot be ignored. According to the drinking water guideline and the TDI, the concentration of DDT and HCH in river water and groundwater sources was ‘marginally safe’. This is a serious health concern. Because this is the first study to report contamination status of pyrethroids and neonicotinoids in this region, it will serve as a baseline for future environmental monitoring and assessment.

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