In this study, residues of organochlorine pesticides (OCPs) in water, suspended particulate matter (SPM), sediment and oysters from the Chanthaburi estuary were monitored closely in the wet and dry seasons for determining potential environmental risks. In water samples, out of twenty OCPs measured, endosulfan and hexachlorocyclohexanes (HCHs) were the two predominant compounds ranging and concentrations between 0.6-13 ng/L and 1-12 ng/L, respectively. Both compounds were found in higher concentrations during the wet season. The two insecticides were significantly correlated with total organic carbon (TOC) in the water with r values of 0.571 (P < 0.05) and 0.440 (P < 0.1), for endosulfan and HCHs respectively suggesting that these chemicals are strongly bound and concentrated by water-soluble organic carbon. As expected, high concentrations of endosulfan and HCHs were associated with SPM and in the surface sediment (0-5 cm) with a concentration ranging from 25-1,219 microg/kg dry wt and 19-110 microg/kg dry wt for SPM, 4-70 microg/kg dry wt and 0.5-50 microg/kg dry wt for surface sediment, respectively. Sediment quality of the Chanthaburi estuary was also assessed in terms of risk to aquatic biota using concentration found in the sediment compared to published allowable threshold levels (U.S. EPA and New York guidelines). Results suggested that most of endosulfan and HCHs levels in sediment samples exceeded the threshold values. Thus potential and environmental risks may be anticipated from levels found in sediment. Oyster from selected farms cultured at the study area appeared to take up both endosulfan and HCHs in proportion to level presented in the water and SPM. The range of endosulfan and HCHs observed in oyster tissue were from 4-46 microg/kg wet wt, and from non-detectable to 8 microg/kg wet wt. respectively. Human risk from oyster consumption was considered by comparing the value measured with allowable threshold level of concerned chemical. The levels of endofulfan and HCHs measured in oyster showed that oysters from this estuary area were safe for consumption.

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The effect of soil supplementation with biosolids at various ratios on fecal-origin microorganism activity was evaluated in a ryegrass sward farm. Fifteen plots with 3 different soil and biosolid mixture ratios were assessed. Soil and grass were sampled over a period of 4 months (days 0, 30, 45, 60, 75, and 120) for soil and on days 75 and 120 for grass, corresponding to first and second grass harvest periods. We analyzed fecal coliforms, somatic phages, helminth eggs, and environmental factors, such as rainfall, temperature, and moisture. The fecal coliforms decreased by 2 logarithmic units (LU) in all soils containing biosolids and by 1 LU in the soil alone and in biosolid control plots alone. The concentration of somatic phages decreased to 2 to 3 LU in the soil containing biosolids and to 1 to 2 LU in the control plots. In contrast, however, there was a noticeable increase in helminth eggs on days 75 ad 120, but not in the soil control alone. Maximum concentrations (10(2) CFU/g TS; colony forming units per gram total solids) of fecal coliforms were found on the grass and in other samples, but the concentrations of phages and helminth eggs were below detection limits. Environmental factors did not significantly influence the results, and grass production increased from 35 to 50 Ton/Ha (tons per hectare) with biosolid supplementation, as compared with controls (14 Ton/Ha).