Influence of Suspended Clay Minerals and Humic Matter on the Solid Phase Extraction Efficiency of Selected Pesticides from Water

The purpose of this investigation was to determine the influence of humic acids (HA) and Ca-montmorillonite (CaM) on the solid-phase extraction (SPE) efficiency of atrazine, alachlor and α-cypermethrin from water samples at various pH-values. The nature and intensity of binding of the studied pesticides to CaM were determined by X-ray diffraction analysis and termogravimetric analysis (TGA) test. The studied pesticides eluted from discs were analysed by thin-layer chromatography (TLC). The effects of CaM and humic acid were generally pH-dependent and acted independently in extraction efficiency influence. Lower recovery of pesticides was observed at higher pH values when CaM was ≥0.1 g and was attributed to greater dispersion of clay, increased surface area and subsequent adsorption. Concentrations of dissolved organic carbon (DOC) in humic acid had less effect on the extraction efficiency when water was at pH 8 compared to water at pH 2, which was probably due to greater nonpolar interactions of the pesticides to the charge-neutralized humic acid molecule.     

Influence of temperature and soil type on the toxicity of three pesticides to Eisenia andrei

Expansion of agriculture in the tropics has increased the use of pesticides that may affect the soil ecosystems. Few studies so far determined the effects of pesticides in the tropics and tropical risk assessment therefore often relies on data from temperate conditions. Hence we compared the toxicity of chlorpyrifos, carbofuran and carbendazim to the earthworm Eisenia andrei at two different temperatures reflecting temperate and tropical conditions. The toxicity of the three pesticides in both conditions decreased in the order carbendazim > carbofuran > chlorpyrifos. For chlorpyrifos and carbofuran, but not for carbendazim, survival was more sensitive at the higher temperature, probably due to increased earthworm activity. Sub-lethal effects (reproduction and growth) however, varied inconsistently with temperature and soil types. We conclude that toxicity of pesticides in tropics may not be predicted from data generated under temperate conditions, even within the same species.     

Use of biomarkers in Nile tilapia (Oreochromis niloticus) to assess the impacts of pollution in Bolgoda Lake, an urban water body in Sri Lanka

The present study reports the first analysis of water pollutants in Sri Lankan waters using a suite of biomarkers in Nile tilapia (Oreochromis niloticus) residing in Bolgoda Lake which receives urban, industrial and domestic wastes from multiple sources. The fish were collected from the lake in the dry period (April 2005) and wet periods (September 2005, October 2006) and the levels of biomarkers viz. hepatic ethoxyresorufin O-deethylase (EROD), glutathione S-transferase (GST), metallothioneins, biliary fluorescent aromatic compounds, brain and muscle cholinesterases (ChE) were compared with those of the laboratory reared control fish and the fish obtained from a less polluted water body, Bathalagoda reservoir (reference site). The results revealed that biomarker levels of the fish collected from the reference site were not significantly different from the controls. Hepatic EROD and GST activities in fish from Bolgoda Lake were induced 4.2-16.6 folds and 1.4-3.3 folds respectively compared with the control fish. Analysis of bile in the lake fish revealed recent uptake of naphthalene, pyrene and benzo(a)pyrene type polycyclic aromatic hydrocarbons (PAHs). The induction of EROD activities in feral fish reflects the exposure of fish to aryl hydrocarbon receptor agonists including PAHs present as pollutants in the Bolgoda Lake. Cholinesterase activity in the fish inhabiting one sampling site of Bolgoda Lake was lower (22-40% inhibition) than the activity measured in the control fish indicating the presence of anticholinesterase pollutants in the area. Hepatic metallothionein levels in the lake fish were higher (1.9-3.2 folds) in comparison to the controls indicating metal exposure. The results support the potential use of these biomarkers in Nile tilapia in assessing pollution in tropical water bodies.     

Chlorpyrifos causes decreased organic matter decomposition by suppressing earthworm and termite communities in tropical soil

Effects of pesticides on structural and functional properties of ecosystems are rarely studied under tropical conditions. In this study litterbag and earthworm field tests were performed simultaneously at the same tropical field site sprayed with chlorpyrifos (CPF). The recommended dose of CPF (0.6 kg a.i. ha⁻¹) and two higher doses (4.4-8.8 kg a.i. ha⁻¹) significantly decreased litter decomposition during the first 3 months after application, which could be explained from lower earthworm and termite abundances during this period. Species-specific effects of CPF on organism abundance and biomass were observed, with termites being mostly affected followed by the earthworm Perionyx excavatus; the earthworm Megascolex sp. was least affected. Recovery was completed within 6 months. Decomposition in the controls and lowest two treatments was completed within 4 months, which suggests the need for modification of standard test guidelines to comply with faster litter degradation under tropical conditions.