K. Raghu

Monitoring of organochlorine pesticide residues in the Indian marine environment

Organochlorine pesticide residues in sediment and fish samples collected from the east and west coasts of India are presented. HCH isomers and DDT and its metabolites are the predominantly identified compounds in most of the samples. Despite the higher quantity of consumption, HCH and DDT levels in fish in India were lower than those in temperate countries suggesting a lower accumulation in tropical fish, which could be due to rapid volatilization and degradation of these insecticides in the tropical environment. The predominance of alpha- and beta-HCH reflect the use of technical grade HCH in India. The high temperature in the tropics also enhances the elimination rate of chemicals in fish, as the biological half-lives of semivolatile compounds such as DDT are short at high temperature.

Effect of temperature on antagonistic and biocontrol potential of Trichoderma sp. on Sclerotium rolfsii.

Sclerotium rolfsii is a destructive soil-borne and postharvest plant pathogen. Use of the antagonistic fungus Trichoderma sp. has been earlier reported by us to successfully control this pathogen under postharvest conditions. In the present paper we report on the effects of temperature on the growth and biocontrol potential of Trichoderma sp. on S. rolfsii. Experimental results indicated that S. rolfsii and Trichoderma sp. have different temperature optima for growth: 30–35 °C for the pathogen and 25–30 °C for the antagonist. In dual culture, Trichoderma overgrew S. rolfsii at 25 °C and 30 °C, but at 35 °C and 37 °C, S. rolfsii overgrew the colony of Trichoderma. Trichoderma produced higher concentration of fungitoxic metabolites in broth culture at higher temperatures. In bioassays using ginger slices and whole rhizomes, it has been demonstrated that Trichoderma is not very effective in suppressing S. rolfsii at temperatures above 30 °C. In light of these results, possible mechanisms of biocontrol of S. rolfsii as a postharvest pathogen has been discussed. Storage temperature has been suggested as a critical factor in biocontrol of S. rolfsii.

Studies on degradation of 14C-DDT in the marine environment.

Degradation of 14C-DDT was studied in a marine ecosystem for 60 days and in marine sediments under moist and flooded conditions using a continuous flow system for a period of 130 days. 14C-DDT residues were recovered in sediments of the marine ecosystem at uniform level of 60-65% of the applied 14C-activity throughout the incubation period. DDD was a major metabolite in sediments while DDMU was a major metabolite in clams. Clams brought about substantial degradation of DDT. However, 14C-residues recovered form clams are not suggestive of significant bioaccumulation. In the continuous flow experiment, under both moist and flooded conditions, DDT underwent degradation and about 22% of the applied 14C-activity was recovered as volatiles under both conditions. In sediments, extractable 14C-residues accounted for about 30 and 19% under moist and flooded conditions, respectively. DDT was the major compound in extractable residues as identified by TLC-autoradiographic procedures. More bound residues were formed under flooded than under moist conditions.

Degradation of 14C-carbofuran in soil using a continuous flow system.

14C-carbofuran underwent considerable mineralization (approximately 30% of the applied activity) in Vertisol soil under moist and flooded conditions during 60 days incubation. Bound residues were formed under both the conditions, the extent being more in moist soils (approximately 55% of the applied activity) than under flooded conditions (approximately 41% of the applied activity). 3-Keto carbofuran was the only significant metabolite observed under flooded conditions.

Effect of carbofuran, carbaryl, and their metabolites on the growth of Rhizobium sp. and Azotobacter chroococcum.

Rhizobia and Azotobacter play a conspicuous role in nitrogen cycle of the soil, Seeds of legume crops are coated with rhizobial cells in association with insecticides and fungicides t~ have effective nodulation and seed protection. In addition, rhizobial and azotobacter cells may be exposed to pesticides and their metabolites present in the soil, Carbamate insecticides, carbofuran and carbaryl are widely used for crop protection, Carbofuran is metabolized to 3-hydroxycarbofuran and 3-ketocarbofuran, carbaryl to l-naphthol in soil (Rajagopal et al. 1984) and these metabolic products are known to effect some biological processes more than parent compounds (Lee 1976; Bollag and Liu 1971), The present investigation was aimed at studying not only the effects of carbofuran and carbaryl but also their metabolites viz, 3-hydroxycarbofuran, 3-ketocarbofuran and l-naphthol on the growth of Rhizobium sp, and Azotobacter chroococcum in liquid cultures,

Pesticides‐non target plants interactions: An overview

Pesticides are widely used for crop protection in agriculture, plantation and forestry. Pesticides, when sprayed or dusted in the fields, only a small amount fall directly on the target organisms due to the small size and mobility of the pests. Most of them come to the soil or to the plants by direct precipitation or spray drift. Plants growing in the contaminated soil take up these chemicals along with water and mineral nutrients and translocate them to the aerial parts. Pesticides fallen on the leaf surface may find their way inside through leaf cuticle, stomata, hydrathodes, lenticels or tissues in the bark. Several factors influence pesticide uptake by plants. Pesticides are highly toxic chemicals and may not be absolutely specific in their actions. Impact of pesticide on plant depends upon its absorption, translocation and metabolism within the plant. Pesticides are usually detoxified in plants through series of degradation reactions and conjugation processes forming bound or insoluble residues. Fail...

Mineralization of 14C-labelled rice straw in aerobic and anaerobic clay soils as influenced by insecticide treatments

Abstract The mineralization of 14 C-labelled rice straw in a clay soil under aerobic and anaerobic conditions as influenced by hexachlorocyclohexane, carbaryl and carbofuran was studied for 40 days. More mineralization of 14 C-labelled rice straw was observed in aerobic than in anaerobic soil. HCH at 10-times field rate concentration only inhibited 14 CO 2 evolution in aerobic soil after 3-days incubation. In general, insecticides applied to soil at normal field rates and 10-times field rates had no effect on either the amount of 14 CO 2 evolved or 14 C-residues remaining in the soil.

Uptake and distribution of 14C-carbofuran and 14CHCH IN cat fish

Abstract Uptake and distribution of 14 C-carbofuran and 14 CHCH were studied in a cat fish ( Heteropnenstes fossils ). It was observed that 14 C-carbofuran was taken up and remained in spleen while 14 CHCH was absorbed in muscles of the cat fish for a short period only. It may be concluded that there is no bioaccumulation of both these insecticides in cat fish at the recommended field application rates.

Photolysis of thiabendazole in aqueous solution and in the presence of fulvic and humic acids

Abstract Irradiation of thiabendazole in aqueous solution at λ ≥ 290 nm resulted in 91.6% substrate transformation in 4 h. The degradation approximately followed first order kinetics; rate constant, 1.73 × 10−4 s−1 and half-life, 1.01 h. Irradiation under UV-light (λ ≥ 290 nm) in the presence of fulvic and humic acids (isolated from soil, Scheyern, Germany) resulted in 90.8% and 88.4% degradation of the chemical respectively. Several products were isolated and their structure determined by GC-MS. Humic and fulvic acid seem to have little effect on photolysis of thiobendazole in water.