RESUMEN
Fenobucarb is one of most common insecticides applied to rice crops in the Vietnamese Mekong Delta. Paddy fields are preferred habitats for snakehead fish (Channa striata). Therefore, the probability of exposure risks and growth effects is highly. This paper aimed to examine the effects of using fenobucarb based - Excel Basa 50EC on the brain cholinesterase (ChE) of snakehead fish. Two rice fields, in which a single dose of Excel Basa 50EC was applied to one field, whilst the other acted as a control. Each field was subdivided into three plots by earthen dikes. In each plot, one fish cage (1.2 m x 1.2 m x 1.2 m) was installed that was stocked with 20 snakehead fish. The Excel Basa 50EC was applied once at the indication dose. The results highlighted that the concentration of fenobucarb in water at 1 hr after application was 116.72 ppb ± 12.64, which decreased to 23.96 ± 6.61 ppb after d and then to below detection limits (0.02 ppb). For fish living in this field, no mortality was seen, but ChE was significantly inhibited for 31 % on the first day and recovery following 7 days of exposure. Residues of fenobucarb in soil and fish should also be investigated furthermore.
RESUMEN
Public concern in Vietnam is increasing with respect to pesticide pollution of the environment and of drinking water resources. While established monitoring programs in the Mekong Delta (MD) focus on the analysis of organochlorines and some organophosphates, the environmental concentrations of more recently used pesticides such as carbamates, pyrethroides, and triazoles are not monitored. In the present study, household level pesticide use and management was therefore surveyed and combined with a one year environmental monitoring program of thirteen relevant pesticides (buprofezin, butachlor, cypermethrin, α-endosulfan, ß-endosulfan, endosulfan-sulfate, fenobucarb, fipronil, isoprothiolane, pretilachlor, profenofos, propanil, and propiconazole) in surface water, soil, and sediment samples. The surveys showed that household level pesticide management remains suboptimal in the Mekong Delta. As a consequence, a wide range of pesticide residues were present in water, soil, and sediments throughout the monitoring period. Maximum concentrations recorded were up to 11.24 µg l(-1) in water for isoprothiolane and up to 521 µg kg(-1) dm in sediment for buprofezin. Annual average concentrations ranged up to 3.34 µg l(-1) in water and up to 135 µg kg(-1) dm in sediment, both for isoprothiolane. Occurrence of pesticides in the environment throughout the year and co-occurrence of several pesticides in the samples indicate a considerable chronic exposure of biota and humans to pesticides. This has a high relevance in the delta as water for drinking is often extracted from canals and rivers by rural households (GSO, 2005, and own surveys). The treatment used by the households for preparing surface water prior to consumption (flocculation followed by boiling) is insufficient for the removal of the studied pesticides and boiling can actually increase the concentration of non-volatile pollutants.