Levels of DDT and HCH in Sediments

The data on the accumulation of pesticides in marine sediments is limited, especially considering the length of India's coastline. We have chosen Sundarban mangrove wetland, which is located in the estuarine part of Hugli River, as an example to demonstrate the pollution status of Indian coastal systems with these contaminants. Guzzella et al. (2005) documented distribution of various organochlorine pesticides in the surface sediments (<63 mm particle size) along the stretch of the Ganges (Hugli) estuary including Sundarban mangrove wetland, eastern coastal part of India (Fig. 10.2). The results revealed a wide range of spatial variations. The range of concentrations of HCH, HCB, DDT and PCBs in the sediments were 0.11-0.40, <0.05-0.98, 0.18-1.93 and 0.18-2.33 ng g-1 dry wt, respectively. The presence of HCH isomers and DDT and its metabolites can be attributed to the use of these insecticides in agriculture as well as anti-malaria sanitary activities carried out throughout the country due to their cost benefits, bioefficacy potential, and popularity among the farmers (Pandit et al. 2002). HCH pesticide has been used for agricultural purposes to control insects in cotton, rice, and vegetable crops and is still used in some of the developing countries around the tropical belt (Doong et al. 2002). The concentration of four important isomers of HCHs (a, b, g and 8) reveals a heterogenic nature of distribution. The composition of HCH isomers a- and g-HCH (lindane) was detected in all the samples, whereas b- and 8-HCH were below the detection limits in majority of the cases (the limit of detection was 0.02 mg l-1 for each PCBs, 0.2 mg l-1 for each HCH insecticide and 0.05 mg l-1 for each DDT). This may be relative to isomerization of HCHs during the process of transport and transformation in a marine ecosystem (Iwata et al. 1994; Dou and Zhao 1998). The aisomer was the predominant one followed by g - isomer, reflecting the use of a technical mixture of HCHs (Kannan et al. 1995). a - HCH has higher values (0.26 ng g-1 dry wt) of Henry's law constant and vapor pressure than b--HCH and g -HCH, indicating greater efficiency by atmospheric transport of a -isomer than other isomers (Iwata et al. 1994) favoring existence of the isomer in all the samples. The ratios of a - to g -isomer were well below those in the technical mixture (i.e., 4-7). The low HCH ratio in the sediment sample implies the use of lindane in this region. HCH contamination might have occurred through atmospheric transport

Sundarban India
Fig. 10.2 Map showing the sampling locations in the lower stretch of the Hugh estuary and Indian Sundarban mangrove delta

from others parts of India where a large amount of technical HCHs is still being used and high concentrations were found in biota (Ramesh et al. 1992). Recently, Sarkar et al. (2008) reported the first comprehensive account of the organochlorine pesticide residues (HCHs, DDTs etc.,) in core sediments (<63 mm particle size) from the mudflat of Sundarban wetland, which revealed an erratic pattern, either top to bottom or vice versa, reflecting non-homogenous input of these compounds. DDTs were detected in all sediment samples, but the contribution of individual metabolites showed differences. pp'-DDT and op'-DDT were found to be much more significant than DDE and DDD. The occurrence of DDT isomers is predominant in the following order: pp'-DDT > pp'-DDD > pp'-DDE > op'-DDT > op'-DDD > op'-DDE. The dominance of DDTs in the sediment compared to DDT metabolites was also reported by Pandit et al. (2002) from the coastal marine environment of Mumbai, western part of India. This may be attributed to the slow degradation of DDTs or recent input of DDTs in this environment (Tavares et al. 1999; Yuan et al. 2001). The dominance of either pp'-DDT or both pp'-DDT and pp'-DDE in sediments was also recorded by Guruge and Tanabe (2001) from the west coast of India and by Booij et al. (2001) from the northwest coast of Java, Indonesia.

According to Strandberg et al. (1998), the ratio of pp'-DDT/ pp'-DDE provides a useful index to know whether the DDT input at a given site is recent or happened in the past, a value <0.33 generally indicates an aged input and an overall value of >0.33 was found in majority of sediment samples along the east coast of India, indicates recent inputs of DDT. The contribution of pp'-DDT over 50% of the total DDT along the coast seems to be associated with vegetable growing activities. The use of pesticides in agriculture and aquaculture has generally been increasing due to rising population and demand for more agrochemicals at these sites. The Hugli (Ganga) River passes through relatively dense industrial and residential areas (Fig. 10.2) where pesticides are sprayed during the public health campaign against malaria and also for other purposes. The relative concentration of the parent DDT compared to its biological metabolites, DDD and DDE can be used as indicative indices for assessing the possible pollution sources. The high percentage composition of op'-DDT and pp'-DDT with respect to total DDT clearly illustrates that DDT usage has not been eradicated yet in the country, and there might be fresh input of DDT to the coastal estuary, which was also observed by Babu Rajendran et al. (2005) in sediments of Chennai harbor and Cuddalore fishing harbors, south east coast of India. India is ranked the biggest consumer and manufacturer of HCH and DDT in the world (Mehrotra 1993) as these are cheap as well as effective chemicals (Bashkin 2003). Sarkar and Sen Gupta (1987) measured the pesticide residues in sediments along the west-central coast of India in the Arabian Sea showing the following decreasing order: HCH > pp'-DDE > pp'-DDT > op'-DDE > pp'-DDD. Among the metabolites of DDT, residues of pp'-DDE and op'-DDE are known to be much more significant than DDD in the marine environment. In the east and west coast of India, Pandit et al. (2001) observed that HCH isomers and DDT and its metabolites are the predominantly identified compounds in majority of the surface sediment samples. The predominance of a- and b-HCH reflects the use of technical grade HCH in India. An overall low level of DDT, DDD and DDE residues in sediments were recorded in sediments where DDE followed by DDT constituted the bulk portion. Comparable residue levels of these pesticides have earlier been reported in the Indian marine environment (Sarkar and Sen Gupta 1987; Sarkar and Sen Gupta 1988a, b, c). They attributed that the significant concentrations of DDE in the coastal sediments to the presence of various kinds of marine benthic organisms, which

Table 10.1 Comparison of organochlorine concentrations in sediments from coastal regions in Asia (ng g-1 dry weight, n.d = not detectable)

Location

Year

DDTs

HCH

Reference

Mason Bay, Korea

1997

0.2-80.2

nd-1.3

Hong et al. (2003)

Ulsan Bay, Korea

2001

0.02-41.9

0.02-4.55

Khim et al. (2001)

Wu-Shi estuary, Taiwan

2002

nd-11.4

Doong et al. (2002)

Daya Bay, China

1999

0.10-20.3

0.3-4.2

Zhou et al. (2001)

Minijiang River Estuary,

1999

1.6-13.1

3-16.2

Zhang et al. (2003)

China

Yangtze Estuary, China

2001

nd-0.6

Liu et al. (2003)

Singapore coast

2003

2.2-11.9

3.3-46.2

Wurl and Obbard (2005)

West coast of India

1995-1997

nd-364

1.5-1053

Pandit et al. (2001)

accelerates the biodegradation process and the alkaline nature of marine systems which is highly favorable for such types of transformations (Pandit et al. 2001). To evaluate the relative degrees of OCP contamination in coastal sediments in India, a comparison has made against the available data in Asian context as shown in Table 10.1. The comparison study is compromised by the fact that different studies considered different DDT metabolites and it is still important to evaluate the OC contamination to get a sense of regional similarity. It is evident that the Indian coastal regions present low to moderate OC contamination in sediments. The highest values for both, total DDT and total HCH, in Indian coastal environments are higher than in other Asian countries referring to Table 10.1. Sarkar et al. (1997a, b) found higher mean concentration of £DDT and dieldrin (by factors of 1.7 and 2.4 respectively) in estuarine sediments of the Arabian Sea areas compared to offshore sediments while mean concentrations of £HCH, aldrin, and endrin were similar for both offshore and estuarine samples. In both offshore and estuarine sediments, a-HCH was the most dominant isomer and for the DDTs, pp'-DDE was the most predominant metabolite except near Cannanore and Murmugao (west coast of India) where op'-DDE and pp'-DDT were significant in offshore samples. Their overall assessment revealed that Zuari and Kali estuaries, west coast of India, are the most susceptible to DDT as compared to other estuaries. Sarkar and Sen Gupta (1988a, b) determined residues of organochlorine pesticides in sediments from the Bay of Bengal. The compounds and concentrations detected were aldrin at 20-530 ng g-1 (all sample weights expressed as ww), g-HCH at 10-210 ng g-1, dieldrin at 50-510 ng g-1 (Sarkar and Sen Gupta 1988a, b), and £DDT at 20-790 mg g-1 (Sarkar and Sen Gupta 1988a, b) . The total DDT concentration in offshore sediments of Chennai, southeastern part of India, ranged between 0.3 and 1.18 ng g-1, the maximum concentration was 670-103 times lower than the highest concentration reported by Sarkar and Sen Gupta (1988a, b, c) This reveals that, during the 10 year period the DDT burden in the marine environment has drastically declined, clearly indicating that DDT usage in India has decreased and the restrictions imposed by Indian government is effective in containing use of POPs. A decreasing trend of DDT in coastal atmospheric air from east coast of India has been reported earlier by Babu Rajendran et al. (1999). Similarly, Monirith et al. (2000) also reported an obvious decline of HCHs and DDTs concentrations in the green mussel Perna viridis, bivalve mollusca, from the east coast of India during 1988-1989, 1994-1995 and 1998.

The variability in pesticide residue concentrations is attributed to the presence of numerous rivers along the east coast of India, which includes the Hugli, Mahanadi, Vamsodhara, Godavari, Krishna, Pennar and Palar Rivers, (Fig. 10.1). All these rivers bring copious amount of agricultural discharges containing persistent organic pollutants including organochlorine pesticides and drains into the Bay of Bengal. Among the metabolites of DDT, both pp'-DDE and op'-DDE were consistently found along the east coast of India, which is attributed to the degradation of DDT to DDE in the coastal sediments. Sarkar and Sen Gupta (1988a, b) suggested that the following phenomenon, either individually or in combination, are responsible for the degradation of DDT to DDE: the alkaline nature of the marine system the presence of chemical constituents and their characteristics, e.g. salinity, clay mineral concentration, major elements and the presence and concentration of organic matter; and stored thermal energy in ocean waters, DDT isomers and their metabolites were detected in the sediments of coastal Bay of Bengal in the following order: op'-DDE > pp'-DDE > pp'-DDT > op'-DDD > pp'-DDD > op'-DDT.

Concentration of DDT was in the range of 1.8-25.8 ng g-1 ww and HCH in the range of 0.4-7.1 ng g-1 dw in sediment samples of Vellar Estuary as reported by Venugopalan and Rajendran (1984) . The higher concentration of residues, especially £DDT, in the Bay of Bengal is attributed to the rapid transportation by rivers of their high-suspended sediment load (about 8.1 mg l-1) compared to the rivers draining into the Arabian Sea, where suspended particulate loads are 1.6 mg l" 1 (Shailaja and Sarkar 1992). Several studies have measured the pesticide concentration of sediment of Indian rivers, which includes the Vellar, Ganges, Cauveri and Mahanadi. Ramesh et al. (1991) found higher sediment loads of DDTs and HCHs in the Vellar River during the wet season (3, 4 and 12.4 ng g-1 dw, respectively) compared to dry season (1.0-2.3 ng g-1 dw, respectively). Senthilkumar et al. (1999) found mean sediment concentrations in the Ganges of 5.6 and 2.6 ng g-1 dw DDT and HCH, respectively. Chlorinated pesticide residues in surface sediments from the River Cauvery, in the southeastern coast of India were reported by Babu Rajendran and Subramanian (1999). Total DDT was low and showed no wide variations among sampling sites, which reflect its ban on the use of agriculture to mosquitoes control use. The concentrations of HCHs (39.4-158.4 ng g-1 dw) at various collection sites reflected its agricultural use, with peak values affirming the application of HCH for paddy crops during the monsoon and subsequently to grams during the post-monsoon season. Iwata et al. (1994) analyzed air, river, water, and sediment samples from eastern and southern Asia (India, Thailand, Vietnam, Malaysia and Indonesia) and Oceania (Papua, New Guinea and the Solomon Islands) for the presence of OC pesticides to elucidate their geographical distribution (Fig. 10.1). The distribution patterns in sediments showed smaller spatial variations on global terms, indicating that OCs released in the tropical environment are dissipated rapidly through air and water and retained less in sediments. They noted that the atmospheric and hydro-spheric concentrations of HCHs and DDTs in the tropical developing countries were higher than those observed in the developed nations. There are only a few studies on the fate and behavior of OP pesticides in the marine sediments (Sarkar and Sen Gupta 1985,1986; Sujatha and Chacko 1991) from Indian waters. The low stability of these pesticides in sea sediments indicates that the presence of major element cations have reduced the toxic effects of these pesticides in marine environment (Sarkar and Banerjee 1987) . It is known that OCs are relatively stable in marine sediments. DDT and DDE were even detected in the Arabian deep sea to which they were transferred with sinking particles. There is a striking contrast in pesticide residue concentrations in sediments of the east and west coasts of India. Sediment samples of the east coast contain pesticide residue concentrations in magnitude higher than samples from off the west coast of India the cause of which might be attributed to several factors. All the major Indian rivers flow towards east and drain through fertile agricultural lands and thus receive a considerable input of pesticides, and carry their sediment loads to marine waters on the coast. Also, the use pattern of pesticides shows a predominance of pesticides to lands bordering the eastern coast. The significant role of the sediment quality characteristics (e.g., texture and total organic matter) controlling the leaching process in sediments was emphasized by James and Ramesh (2002). In general, fine grained sediments inhibit pesticide leaching, because of low permeability or higher surface area and enhance the adsorption of pesticides. They established correlation between grain size and organic matter in surface sediments of a river basin of south India. They had also observed a relatively high concentration of g-HCH near the agricultural non-point source area and b-HCH was always higher than gamma- HCH confirming the characteristic feature of b HCH as stable and resistant to microbial degradation (Rajendran and Subramanian 1997). Recently, Sarkar et al. (2008) established negative correlations for all the organochlorines (HCH, DDT etc.,) with sand in core sediments from the Indian Sundarban wetland which reveals that the coarse particles have less adsorption capacity for OCs.

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