Effects of metsulfuron-methyl on aquatic plant (Lemna gibba L.) and recovery from after prolonged exposure under rice cropping conditions

Abstract

The effects and potential recovery of aquatic plant Lemna gibba exposed to a sulfonyl urea herbicide metsulfuron-methyl (MSM) for 120 days under rice cropping condition was investigated. The frond number was decreased by day 15 at the concentration 11 {micro}g/L and 100% inhibition on growth rate of Lemna was observed. Continuous decrease of frond number by day 50 at below the detectable level of residues exhibited symptoms (chlorosis) of MSM toxicity. Toxicity was assessed on the basis of toxicity index (TI) value, growth rate, yield and pigment contents (chlorophyll, carotene, total carotenoid and xanthophyll) of treated samples compared with untreated control. The observed value of 0.698 {micro}g/g chlorophyll a, 0.263 {micro}g/g chlorophyll b, 0.147 {micro}g/g carotene, 1.620 {micro}g/g total carotenoid and 1.473 {micro}g/g xanthophyll contents in treated samples was statistically significantly different from control value of 4.366 {micro}g/g chlorophyll a, 3.132 {micro}g/g chlorophyll b, 0.796 {micro}g/g carotene, 17.755 {micro}g/g total carotenoid and 16.937 {micro}g/g xanthophyll contents by day 50 samples. After prolonged exposure, growth rate, yield and pigment content for the treated samples recovered to control levels on day 120. The obtained data indicate the application of aquatic plant Lemna gibba as sensitive biomarker of water quality as well as the significance of selected biological parameters in the reliable assessment of toxic potential of MSM under rice cropping condition.