A. Ramesh

Distribution and behaviour of persistent organochlorine insecticides in paddy soil and sediments in the tropical environment: a case study in South India.

Paddy soil and sediment samples collected from the Vellar River watershed, Tamil Nadu state, South India from December, 1987 to January, 1989 were analysed to understand the comprehensive behaviour of organochlorine insecticides (HCH and DDT) in the tropical environment. HCH (BHC) showed higher levels in soil during wet season, reflecting the application of technical HCH largely during the flowering season of rice. On the other hand, DDT residues were low and did not show a significant seasonal trend in soil or sediment, indicating small quantities of DDT utilized at present for agricultural purposes in India. When compared to soil, the residue levels in sediments are low and the seasonal variation is less pronounced. This indicates that in tropical watersheds, the relative flux of residues into the aquatic environment is smaller than the amount volatilized to the atmosphere.

Persistent organochlorine residues in dolphins from the Bay of Bengal, South India

Abstract Blubber samples of 12 accidentally netted dolphins from the coastal waters of Porto Novo, southeast coast of India were monitored to assess the persistent organochlorine (HCHs, DDTs, PCBs, and HCB) contamination in these animals. ΣDDT concentrations ranked first, followed by PCBs, ΣHCH, and HCB. HCHs were detected for the first time in dolphins from the tropical waters. The variations in residue levels could be attributed to the physicochemical and biochemical properties of the above compounds. International comparison of residue levels in cetaceans in the recent decade revealed that DDT concentrations in Indian dolphins were comparable to those from other localities whereas PCB levels were low. The continuing contamination by these persistent organochlorines and their toxic effects in tropical cetacean species is predicted in the future.

Characteristic trend of persistent organochlorine contamination in wildlife from a tropical agricultural watershed, south India.

The residue levels of persistent organochlorines, such as HCH (BHC: 1,2,3,4,5,6-hexachlorocyclohexane) isomers, DDT [1,1,1-trichloro-2,2-bis (p-chlorophenyl) ethane] compounds, PCBs (polychlorobiphenyls) and HCB (hexachlorobenzene), were measured in wildlife. The wildlife were sampled from terrestrial and aquatic habitats in and around the agricultural watershed of Parangipettai, South India. On the basis of overall concentrations ∑HCH ranked first followed by ∑DDT, ∑PCB and HCB, reflecting the increasing usage of HCH in recent years in India. The residue levels of organochlorines in birds varied according to their feeding habits and showed the following pattern: inland piscivores and scavengers > coastal piscivores > insectivores > omnivores > granivores. High levels of HCH and DDT residues were recorded in Pond heron and Cattle egret which feed in the agricultural fields. Comparison of HCH concentrations in fish and birds in the study area to other locations was made to further understand the dynamics of contaminant accumulation in tropical wildlife. Regarding birds, a wide variation in residue levels could be seen among various countries, with tropical regions registering high levels. In contrast, the variation is not prominent in the case of fish. The residue levels in fish measured in the present study were generally comparable to values reported from other locations. This suggests that the bioavailability of contaminants to the aquatic fauna is less due to the smaller flux and shorter residence time of these chemicals in the tropics.

Fate of the insecticide HCH in the tropical coastal area of South India

Abstract The residue levels of the insecticide HCH in Vellar estuary, Tamil Nadu, South India were surveyed along with the physical structure of estuary and its hydrokinetic parameters to assess the transport of contaminants in tropical coastal areas. From the flux model it was estimated that most of the HCH applied to the catchment area of Vellar river is removed to the air and only a small part of it was drained to the sea. Compared to the present situation, the flux of HCH to the sea seems to be much larger in the past when the river structure was different from the present. This implies that at present the localized contamination of HCH in the sea is reducing: instead more rapid contamination is advancing on global terms due to the ‘long-range atmospheric transport’ of residues from the ‘point-source’ areas.

Persistent organochlorine residues in green mussels from coastal waters of South India

Green mussels (Perna viridis) collected from nine locations along the South Indian coast were used as bioindicator to assess the organochlorine contamination (HCHs, DDTs, and PCBs) in the coastal environment of South India. Concentrations of ΣHCH and ΣDDT were found to be similar, ranging from 3 to 39 ng g−1 on wet wt basis. On the other hand, PCB levels were apparently lower, varying from <1.0 to 7.1 ng g−1 wet wt. The residue pattern of organochlorines in mussels are principally similar to those in Indian human samples, reported earlier. The coastal marine pollution by HCH in India ranks among the highly contaminated areas in the world.

Fate of HCH (BHC) in tropical paddy field : application test in South India

Abstract A HCH (BHC) application test was conducted in an experimental paddy field in the Vellar river watershed, Tamil Nadu state, South India. Interestingly, most of the HCH applied to the field was found to volatilize rapidly as low residue levels in water, rice plant and soil were recorded. After two weeks of an application, more than 90% of the HCH was found in the air and less than 10% in water, soil and rice plants, thus emphasizing that post-application volatilization is a major route for transport of insecticides to and through the atmosphere in tropical paddy areas.

Persistent Organochlorine Insecticide Residues in Some Paddy, Upland and Urban Soils of India

Abstract A wide variety of agricultural soils from different regions of India such as paddy, wheat, mustard, potato, cotton, tea, tomato, sugarcane, grape and urban soils were surveyed for the residual levels of persistent organochlorine insecticide residues in 1988 and 1989. DDT and HCH concentrations were found to be higher in upland soils and lower in paddy field soils. These results indicate the large application of HCH and DDT compounds for agricultural purposes in India. In urban soil DDT levels were higher than HCHs reflecting the use of the former insecticide in relatively large amounts for vector control. Among DDT compounds, p,p′-DDE showed higher percentage in paddy and upland soils. On the other hand, p,p′-DDT contributed to higher levels in urban soils. The β-HCH was detected as the dominant isomer in both agricultural and non agricultural soils. The levels and percentage compositions of DDTs and HCHs revealed the extent of environmental contamination caused by the continuous usage of persist...