N.B.K. Murthy

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.

Bioremediation of DDT in soil by genetically improved strains of soil fungus Fusarium solani.

Bioremediation of DDT in soil by genetically improved recombinants of the soil fungus Fusarium solani was studied. The parent strains were isolated from soil enriched with DDD or DDE (immediate anaerobic and aerobic degradation products of DDT), as further degradation of these products are slow processes compared to the parent compound. These naturally occurring strains isolated from soil, however, are poor degraders of DDT and differed in their capability to degrade its metabolites such as DDD, DDE, DDOH and DBP and other organochlorine pesticides viz. kelthane and lindane. Synergistic effect was shown by some of these strains, when grown together in the medium containing DDD and kelthane under mixed culture condition. No synergism in DDE degradation was observed with the strains isolated from enriched soil. DDD-induced proteins extracted from individual culture filtrate (exo-enzyme) when subjected to SDS-Polyacrylamide Gel Electrophoresis (SDS-PAGE) showed complementary polypeptide bands in these strains i.e., each strain produced distinct DDD degrading polypeptide bands and the recombinant or hybrid strains produced all of the bands of the two parents and degraded DDD better than the parental strains. Recombinant hybrid strains with improved dehalogenase activity were raised by parasexual hybridisation of two such complementary isolates viz. isolate 1(P-1) and 4(P-2) showing highest complementation and are compatible for hyphal fusion inducing heterokaryosis. These strains are genetically characterised as Kel+BenRDBP-Lin- and Kel-BenrDBP+Lin+ respectively.Recombinants with mixed genotype, i.e., Kel+BenRDBP+Lin+ showing superior degradation quality for DDT were selected for bioremediation study. Recombination was confirmed by polypeptide band analysis of DDD induced exo-proteins from culture filtrate usingSDS-Polyacrylamide Gel Electrophoresis (PAGE) and RAPD (Random Amplified Polymorphic DNA) of genomic DNA using PCR (Polymerase Chain Reaction) technique. SDS-PAGE showed combination of DDD induced polypeptide bands characteristic of both the parents in the recombinants or the hybrids. PCR study showed the parent specific bands in the recombinant strains confirming gene transformation.

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.

Studies on degradation of 14C-chlorpyrifos in the marine environment

Degradation of 14C-chlorpyrifos was studied in a marine ecosystem for 60 days and in marine sediment under moist and flooded conditions using a continuous flow system allowing a total 14C-mass balance for a period of 40 days. In the marine ecosystem, 14C-chlorpyrifos underwent rapid degradation and very little (1-2%) 14C-residues of the applied activity were detected after two months in sediments. Clams were major component of the ecosystem and played a significant role in degradation of the insecticide. In the continuous flow system chlorpyrifos did not undergo substantial mineralization. Volatilization accounted for 0.8-1% loss during first ten days of application. The amounts of extractable 14C-activity were higher in flooded sediments than in moist sediment. More bound residues were formed under moist conditions. TCP (3,5,6-trichloro-2-pyridinol) was the major degradation product formed under both moist and flooded conditions, its formation being higher in the latter conditions. These studies underline the role of clams in degradation of chlorpyrifos and lack of microbial degradation. In absence of clams, chlorpyrifos underwent abiotic degradation in marine sediment with formation of bound residues.

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,

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.

Studies on the Behavior of 14C-chlorpyrifos in a Model Rice Ecosystem

Fate of 14C-chlorpyrifos was studied in a model rice ecosystem. The level of 14C-residues in floodwater showed initially a rapid decline in first 10 days. These residues were observed till 30 days. The insecticide residues in soil did not show any appreciable build-up, thereby indicating that the residue levels of this insecticide may not be significant. Extractable residues were formed up to 10–13% of the applied 14C-activity during the period of 136 days, while the bound fraction of 14C-residues reached a maximum of 2.9% after 92 days. Algae and rice plants showed 14C-residues to the extent of only 0.01% of the applied 14C-activity. Rice grains did not show any residues at all. These results indicate that chlorpyrifos undergoes considerable degradation in rice soils and does not leave residues, which may be of environmental concern.

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.