Mechanistic insights into the relative contribution of sorption and biodegradation on the removal of the herbicide isoproturon (IPU) are reported. ¹⁴C-radiorespirometry indicated very low levels of catabolic activity in IPU-undosed and IPU-dosed (0.1, 1, 100 μg L⁻¹) river water (RW) and groundwater (GW) (mineralisation: <2%). In contrast, levels of catabolic activity in IPU-undosed and IPU-dosed river sediment (RS) were significantly higher (mineralisation: 14.5–36.9%). Levels of IPU catabolic competence showed a positive log-linear relationship (r² = 0.768) with IPU concentration present. A threshold IPU concentration of between 0.1 μg L⁻¹ and 1 μg L⁻¹ was required to significantly (p < 0.05) increase levels of catabolic activity. Given the EU Drinking Water Directive limit for a single pesticide in drinking water of <0.1 μg L⁻¹ this result suggests that riverbed sediment infiltration is potentially an appropriate ‘natural’ means of improving water quality in terms of pesticide levels at concentrations that are in keeping with regulatory limits.

PURPOSE: Isoproturon, a herbicide belonging to the phenylurea family, is widely used to kill weeds in soils. Recent study indicated that isoproturon has become a contaminant in ecosystems due to its intensive use, thus bringing environmental risks to crop production safety. Salicylic acid (SA) is one of the components in plant defense signaling pathways and regulates diverse physiological responses to biotic and environmental stresses. The purpose of the study is to help to understand how SA mediates the biological process in wheat under isoproturon stress. METHODS: Wheat seeds (Triticum aestivum, cv. Yangmai 13) were surface-sterilized and placed on moist filter paper for germination. After 24 h, the germinating seeds were placed on a plastic pot (1 L) containing 1,120 g soil mixed with isoproturon at 4 mg kg−1 soil. After 4 days, wheat leaves were sprayed with 5 mg L−1 SA. The SA treatment was undertaken once a day and lasted for 6 days, when the third true leaf was well developed. For control seedlings, only water was sprayed. Seedlings were grown under a light intensity of 300 µmol m−2 s−1 with a light/dark cycle of 12/12 h at 25°C, and watered to keep 70% relative water content in soils. RESULTS AND DISCUSSION: We investigated the role of SA in alleviating isoproturon-induced toxicity in the food crop wheat (T. aestivum). Plants exposed to 4 mg kg−1 isoproturon showed growth stunt and oxidative damage, but concomitant treatment with 5 mg L−1 SA was able to attenuate the toxic effect. Isoproturon in soils was readily accumulated by wheat, but such accumulation can be blocked significantly by SA application. Treatment with SA decreased the abundance of O2 .− and H2O2, as well as activities of antioxidant enzymes, and increased activities of catalase in isoproturon-exposed plants. The enzyme activities were confirmed by the native polyacrylamide gel electrophoresis. Further, an RT-PCR-based assay was performed to show that several transcripts coding antioxidant enzymes were increased with isoproturon but decreased by SA. CONCLUSION: The present results indicate that exogenous SA is able to improve the wheat tolerance to isoproturon toxicity.