The Effects of Paraquat Used in Upland Rice and Maize Fields on Biomass of Attached Algae

Abstract

Paraquat is a kind of herbicide widely used among Thai farmers especially those working in upland rice and maize fields in steep slope areas. In the rainy seasons, runoff water and sediment contaminated with paraquat drain into streams. This study, aimed to investigate the effects of paraquat, in concentrations of 0, 0.0276, 0.276, 2.76, 27.6, and 276 mg/l on the biomass of attached algae; the primary producers in an aquatic food chain. To conduct the experiment, the algal biomass was measured by the synthesis of chlorophyll a and c of the attached algae in six microcosms. Each microcosm was filled with water samples and attached algae from Mae Kham Stream in Mueng District, Phrae Province. The results of the study show that attached algae exposed to paraquat with concentrations ranging from 0.0276 to 0.276 mg/l synthesized less chlorophyll a and c than the control group that encountered 0 mg/l of paraquat. (The data represented a statistical significance of P < 0.01.) Regarding those exposed to paraquat concentrations of more than 2.76 mg/l, their biomass was adversely affected. In other words, the synthesis of attached algae was inhibited.All in all, paraquat contamination of fresh water leads to destruction of aquatic organisms, especially phytoplankton and attached algae, which are considered vital producers in aquatic ecosystems.