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The application of agrochemicals in Southeast Asia is increasing in rate, variety and toxicity with alarming speed. Understanding the behavior of these different contaminants within the environment require comprehensive monitoring programs as well as accurate simulations with hydrological models. We used the SWAT hydrological model to simulate the fate of three different pesticides, one of each usage type (herbicide, fungicide and insecticide) in a mountainous catchment in Northern Thailand. Three key parameters were identified: the sorption coefficient, the decay coefficient and the coefficient controlling pesticide percolation. We yielded satisfactory results simulating pesticide load dynamics during the calibration period (NSE: 0.92–0.67); the results during the validation period were also acceptable (NSE: 0.61–0.28). The results of this study are an important step in understanding the modeling behavior of these pesticides in SWAT and will help to identify thresholds of worst-case scenarios in order to assess the risk for the environment. [Copyright &y& Elsevier]

Four plants (corn, pumpkin, sunflower & water morning glory) were tested for their ability to germinate and grow in an alkaline Thai soil contaminated with 0.2-20 mg/kg dry soil of either lindane or alpha-endosulfan, two organochlorine pesticides commonly found in agricultural soils in Thailand. Based on root length assessment, sunflower was the most tolerant to lindane contaminant, while corn was the most tolerant to alpha-endosulfan in the alkaline soil. Base on root dry weight assessment, corn was the most tolerant to both lindane and alpha-endosulfan. Corn was selected to further test its ability to tolerate a mixture of 0.2, 2.0, 20 mg/kg dry soil of lindane and alpha-endosulfan in the alkaline soil. The presence of both pesticides decreased root length of corn but did not affect its shoot and root dry weights. The results suggest that corn is suitable for use in the phytoremediation of alkaline soil contaminated with a mixture of lindane and alpha-endosulfan. [ABSTRACT FROM AUTHOR]

Abstract: Series of experiments, including background sediment elutriate, spiked-sediment elutriate and spiked-water toxicity tests, were carried out to study the effect of dredging on survivability and ecological competence of commercially important shrimp postlarvae of Penaeus monodon Fabricius. The test sediment represented the most contaminated from endosulfan and lindane in the Chantaburi river mouth estuary. The maximum sediment contamination levels were 49.4 μg/kg of endosulfan and 58.1 μg/kg of lindane in dry weight basis. Dose-response studies in static, non-renewal spiked-sediment elutriate toxicity tests revealed that LC 50 (96 h) values for survival effect based on measured concentrations were 0.50 (0.26–0.95) μg/L for endosulfan and 0.92 (0.63–1.34) μg/L for lindane. The LOECs for endosulfan and lindane were 0.141 and 0.429 μg/L, respectively. The NOECs were estimated to be the dissoluted endosulfan and lindane concentrations from the Chantaburi estuary sediment. The effects on phenoloxidase enzyme activity in shrimp postlarvae exposed for sub-lethal to lethal doses in sediment elutriate were not significant (p>0.05) at all tested dose levels. The worst case dissolution concentrations of endosulfan and lindane in the water column upon simulatory dredging in the Chantaburi estuary were found to be toxic to shrimp postlarvae on lethal and sub-lethal effects. The NOECs of respective chemicals (i.e., 0.034 and 0.16 μg/L) shared the same orders of magnitude for corresponding NOECs established for whole salt water aquatic life by the USEPA and “safe” levels calculated by 0.01 safety factor approach. In addition, the significance of multiple pollutant assessments for ecological toxicity testing is highlighted. [Copyright &y& Elsevier]

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 μ g/kg dry wt and 19-110 μ g/kg dry wt for SPM, 4-70 μ g/kg dry wt and 0.5-50 μ g/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 μ g/kg wet wt, and from non-detectable to 8 μ g/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. [ABSTRACT FROM AUTHOR]

Few studies have investigated organochlorine pesticide residue content in freshwater plankton communities in Thailand. As a result, this study looks to examine the concentration of organochlorine pesticide residues in plankton collected from Khlong 7 (canal) at Rangsit agricultural area, central Thailand from June 2006 to February 2007. The results from this study show that plankton communities were composed of microphytoplankton, microzooplankton, and mesozooplankton. The average method recoveries varied from 84% to 103% with a relative standard deviation between 0.20% and 3.72%. The concentrations of organochlorine pesticide residues during a one-year-period were in the range of 0.10–3.65 ng/g wet wt and contained DDT and derivatives > Σ endosulfan > Σ HCH > Σ heptachlor > aldrin and dieldrin > endrin and endrin aldehyde > methoxychlor, respectively. Moreover, the residues of Σ HCH, DDT and derivatives, and methoxychlor were higher during wet season than dry season ( t-test, p ≤ 0.05). [ABSTRACT FROM AUTHOR]

This article presents a study to map and evaluate the factors influencing concentrations of six pesticides in groundwater beneath an agricultural region of central Thailand. Several locations have relatively high concentrations of one or more pesticides. Logistic regression models were significant only for endosulfan and dicofol. Depth and texture were significant independent variables for the endosulfan and dicofol models, respectively. Probability of detecting endosulfan increased for shallower wells. Clusters of relatively high pesticide concentrations warrant localized investigations of groundwater pollution and vulnerability.

The adsorption, desorption, and degradation of endosulfan (1,2,3,4,7,7-hexachlorobicyclo[2,2,l]-2-heptene-5, 6-bisoxymethylene sulfite) in two major tropical soils from Thailand were studied. Each soil-type, Rangsit lowland soils (Rangsit series) and Phrabat upland soils (Pakchong series), were sub-divided into surface or plow layer, 0-20 cm depth, and subsoils, 20-40 cm depth. Adsorption was determined using 24 h batch equilibrium, with five different concentrations of 14C labeled endosulfan ranging from 1.04 to 16.64 ng/mg soils. Adsorption coefficient values (Kads) as by Freundlich's model ranged from 0.02 to 0.20. Higher adsorption coefficients were measured in Rangsit soils as compared to Phrabat soils. Desorption as attributed to hysteresis was also measured. Desorption coefficient values(Kdes) were higher than adsorption (Kads) in each study. Degradation of endosulfan was through microbial process. Little abiotic degradation was measured in sterile soil sample. Measured degradation rates were highest in Phrabat plow layer and subsoil. However, total degradation after 98 days was less than 20% of initialapplication rate. Results indicate that applied endosulfan would be persistent or slow to degrade in the soils studied. [ABSTRACT FROM AUTHOR]

Thai cotton growers yearly face serious pest problems consisting of heavy infestation associated with resistance to pesticides leading to expensive and harmful pest control practices. Thanks to a multi discipline research work carried out from 1991 to 1996, a decision-oriented model for cotton crop management was developed and compared to farmers' practices during the 1988 cotton growing season 1998 in Klang Hat district, Thailand. This model, based on plant monitoring, involved a new cotton cultivar (DORA 11 as a replacement for Sri Samrong 60), seed treatment with imidacloprid (at 3.5 g of a.i./kg of seeds), a threshold-based spray of mepiquat chloride, a cotton growth regulator (Pix at 1.5 l/ha) and a set of rules to selectively control with chemical and biological insecticides the major pests the American bollworm (Helicoverpa armigera Hübner) and the cotton leafhopper (Amrasca biguttula biguttula Ishida). This package was more friendly towards environment than farmers' practices since seed treatment does not harm beneficials at the beginning of cotton growing season while 1 and 5 sprays were saved against respectively the American bollworm and sucking pests and more than 50% of the sprays directed against American bollworms involved biological insecticides (Bacillus thuringiensis toxins potentialized by a low dosage of endosulfan). Threshold-based sprays against the main pests, the use of a cotton growth regulator, earliness of cotton cultivar and seed treatment were accountable for savings in pesticide sprays. Involving a biological insecticide and endosulfan at the beginning of cotton growing season and using the same quantity of active ingredient at each spray during the cotton growing season also improved the management of pyrethroid resistance in American bollworm populations was also. There was no significant difference between yields inside farmers' fields and innovation plots. However, thanks to cheaper pest control practices economic results were better. Lastly few improvements of this package are proposed.