Association between herbicide contamination and reproductive effects in freshwater mussel uniandra contradens in agricultural areas, Nan province

Abstract

Nan Province, in the northern part of Thailand, is a fertile area for agricultural activities. Crop rotations in this area lead to widely uses of agrochemicals especially herbicides. To examine whether an intensive use of herbicide could lead to contamination in aquatic environment, sediment and water samples collected from an agricultural catchment in Nan Province were screened for atrazine (GC-MS), paraquat and glyphosate (HPLC). The results showed that detectable levels of atrazine residue were found in water (<0.01-0.16 µg/mL) and sediment (<0.01-0.23 µg/g) of the reservoir. To examine an extent of contamination in biological samples, a freshwater mussel Uniandra contradens collected quarterly from the reservoir during July 2010 to June 2011 were examined for herbicide contamination by enzyme-linked immunosorbent assay. The results showed that detectable levels of herbicide including atrazine (1.26-88.86 ng/g dry weight), paraquat (23.30-55.97 ng/g dry weight) and glyphosate (5.34-11.90 ng/g dry weight) were found in every mussel examined. Monthly sampling and health monitoring of the mussels showed a seasonal change in condition factor, an indicative of overall health, with a significant negative correlation with atrazine and glyphosate residue in the tissue. Reproductive activities as determined by gross- and microanatomical as well as biochemical markers showed that mature sperms can be found throughout the year, indicating prolonged male gametogenic activities. A similar pattern was observed in female mussels with an exception in dry season when oocytes became larger, the vitellogenin level was at peak and swelling gills with mature egg deposition was evident. These indicatives of a spawning period occurred in dry season when atrazine contamination was evident, indicating a potential window of susceptibility of the mussel reproduction and development. Using U. contradens as a sentinel of contamination in two reservoirs with different agricultural activities, it was further proven that the mussel could be used as an effective biomonitor with a measurable and correlative response to herbicide contamination. The data from this study could be used as an early warning of the effects of herbicide contamination on freshwater animals and maybe used as a potential link to predict the reproductive health risk of other organisms including human living in this area.