The effects of agrochemicals on an aquatic ecosystem : A case study from the Krian River basin, Malaysia

Summary

The existing environment of the Krian River basin in Malaysia is not in its natural form for it has been much developed into agricultural lands (105,000 ha). The growing demand for agricultural lands requires further reclamation of swampy forests, which will result in an increased use of fertilisers (estimated 10 percent increase, from 29,500 t to 32,500 t), weedicide, dalapon (estimated 6 percent increase, from 187,620 kg to 199,530 kg) and pesticides, BHC and thiodan/endosulfan (estimated 2 percent increase, from 312 kg to 318 kg).

Contrary to belief, the concern over increased levels of nitrogenous fertilisers and pesticides concentrations used in the existing agricultural projects is unfounded. The agrochemicals contribute insignificant amounts of contaminants into the aqueous system. Deleterious deterioration of water quality in the waterways is not apparent. The rich assemblage of icthyofauna comprises 14 freshwater fish species, 21 saltwater-freshwater interface species, like the freshwater prawn and marine fishes that have acclimatised to freshwater conditions, and 28 coastal- marine water fish species, two brackish water penaeids and three molluscs of commercial value. However, if the water quality data are used in isolation to interpret the consequences of large- scale usage of agrochemicals, the conclusion is inadequate and may be misleading. The impact of the flow condition in fields, the localised long-term effects like the fate and spatial distribution on the surrounding media (water, sediments and exposed aquatic life), bio-accumulation and bio-magnification should be considered. Though of no acute toxicity to hardy icthyofauna in the Krian Rice Irrigation basin, lipophilic organochlorines pose health risks to consumers of contaminated fishery products from these Krian rice fields.