Polychlorinated biphenyls and organochlorine pesticides in River Brahmaputra from the outer Himalayan Range and River Hooghly emptying into the Bay of Bengal: Occurrence, sources and ecotoxicological risk assessment☆
Graphical abstract
Introduction
Freshwater is the basic need for human survival and the inherent ecosystems support diverse group of flora and fauna. India has 16% of the global population with only 4% of the world’s freshwater. Currently the freshwater quality in India and associated biodiversity are facing serious challenges due to the fast growing economy, increasing industrialization and the large agricultural sector. River Brahmaputra (RB) is a trans-boundary river that enters India in Arunachal Pradesh along the outer Himalayan Range and flows from Assam to West Bengal where it meets River Hooghly (RH), a distributary of River Ganga. RB and RH merges with River Meghna in Bangladesh and before emptying into the Bay of Bengal forms the world’s largest delta, the Sunderban delta shared by the state of West Bengal in India and Bangladesh. RB and RH are two perennial rivers providing perpetual supply of freshwater to the plains of eastern and northeastern states of India to support irrigation, human and industrial consumption. From River Hooghly, nearly 493 million gallons per day is pumped to satisfy water demand in the surrounding region (Rudra, 2007). Central pollution control board reported that 1573 million litres per day (MLD) of sewage is discharged in RH (CPCB, 2008 ). Brahmaputra basin has a population of 29.1 million people utilizing 24 km3 of surface water every year (Sandrp, 2013).
During 2005–2010, 5039 metric tons (MT) and 1191 MT of dichlorodiphenyl trichloroethane (DDT), were used for malaria control in Assam and West Bengal respectively and 17856 MT of endosulfan was produced in India (PPIN, 2013). Synthetic pesticides constituted 85% of the total pesticide demand in the northeastern India and one fourth of those pesticides were organochlorine pesticides (OCPs). Among OCPs, endosulfan was mostly applied in the tea estates (Gurusubramanian et al., 2008). Aldrin and dieldrin were never produced in India but 622 MT of aldrin was imported during 1995–2000 (GEFIO, 2002).
The inventory of electrical equipment containing PCBs estimated 1548 transformers containing pure and contaminated PCBs with total weight of PCB oils to be 10000 MT and the total amount of PCBs is estimated to be 28000 MT in India (Sharma, 2013).
In the recent past, atmospheric OCPs (Chakraborty et al., 2010, Chakraborty et al., 2013) and PCBs (Chakraborty et al., 2013) have been observed in and around Kolkata city along the River Hooghly and the authors of those studies also reported associated re-emission from soil (Chakraborty et al., 2015, Chakraborty et al., 2016). Hooghly estuarine sediment has been found to be contaminated with organic contaminants (Bhattacharya et al., 2003, Guzzella et al., 2005). OCPs may reach the surface riverine water via agricultural runoff, direct applications, spray drift, aerial spraying and erosion (Turgut, 2003, Singh et al., 2007, Zhou et al., 2008).
Soil borne OCP residues have been reported from the north-eastern states of India along the bank of River Brahmaputra (Mishra et al., 2012, Devi and Raha, 2013). Persistent organic pollutants (POPs) like OCPs and PCBs owing to their resistance to degradation, toxicity, bioaccumulation through food chain and their ability for long range atmospheric transport (Erdogrul et al., 2005, Guzzella et al., 2005, Gao et al., 2008) are of serious concern for freshwater quality.
Though India is a signatory for the Stockholm convention (Fiedler, 2008), only limited data is available for such compounds from the surface water of perennial rivers, particularly from eastern and northeastern states of India. Hence in this study we aim to elucidate the occurrence and sources of selected OCPs and PCBs in the surface water of River Brahmaputra from the outer Himalayan Range and lower stretch of River Hooghly before emptying into the Bay of Bengal and estimate the associated risk posed to the inherent freshwater ecosystems.
Section snippets
Study area
Details of the sampling sites have been given in Fig. 1, Table S1 and S2. Surface river water samples were collected using a stainless steel bucket from 16 sites in RB and 20 sites in RH during summer in the month of June 2012 (Fig. 1a and b). For each site, a composite water sample was collected over a length of 500 m from 5 points. Five samples within nearly 9 m2 of each site (each of 1 L) of river water were collected and mixed well to obtain one composite sample for each site. Sampling jars
General discussion
Overall concentration range and spatial distribution of ∑19PCBs and selected OCPs in River Brahmaputra (RB) and River Hooghly (RH) have been given in Table 1 and Fig. 1a & b. ∑19PCBs varied between 39–161 ng L−1 (average ± SD: 83 ng L−1 ± 32) in RB and 57–233 ng L−1 (average ± SD: 116 ng L−1 ± 46) in RH. More than 90% PCBs were comprised of tri and tetra congeners in both the rivers in line with Pearl River, China (Guan et al., 2009). Dominance of tetra congeners were also observed in River
Acknowledgement
This work was supported by the support of SRM University start-up research grant and the Fast Track Research Grant under Young Scientist Scheme funded by the Department of Science and Technology, Government of India (SR/FTP/EE-44/2012). Authors would like to thank Mr. Elvis Dsouza managing partner of EDPC polymer industries Mumbai, for his extensive support during sampling campaign.
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