Effects of the phenylurea herbicide diuron on the physiology ofSaccharina japonica aresch

Abstract

Diuron (N-[3,4-dichlorophenyl]-N,N-dimethylurea), a herbicide belonging to the phenylurea family, is not only widely used to destroy unwanted weeds but is also used as a antifouling agent in paints. This toxicant has a dramatic effect on the aquatic dwellers including seaweeds. This study investigates the effect of diuron on growth, pigment content, chlorophyll fluorescence, and antioxidant capacity ofSaccharina japonica, a brown seaweed occurring in South Korea. Significant (p<0.001) reduction in fresh weight and area were observed after a fortnight of exposure to diuron (0.1-0.4 mg/L diuron). Increasing concentrations of diuron caused reduction in the carotenoid content, whilst comparatively lower reduction in chlorophyll a content were observed within the concentrations tested i.e. 0.1–0.4 mg/L diuron. Chlorophyll a fluorescence parameters revealed a slight increase in minimal (Fo) and maximal (Fm) fluorescence yield up to 0.025 mg/L; further increase in diuron concentration caused significant reduction in the mentioned parameters. A concentration dependent decrease in the optimal quantum yield (Fv/Fm) as well as the maximum electron transport rate (ETRmax) was recorded with increasing diuron concentrations; except for the fact that, no electron transport was evidenced at 0.4 mg/L. Concentration dependent decline in the DPPH radical scavenging activity was also observed. The generation of high levels of reactive oxygen species probably decreased the non-enzymatic antioxidant defense system inS. japonica. Based on this investigation, it could be stated that diuron dramatically influenced the physiology and growth of the seaweedS. japonica. Further, this study ascertains the negative impact of diuron contamination, from terrestrial (agricultural) and marine (antifouling paints) sources, on the marine dwellers. AsS. japonica is highly sensitive to diuron, it demonstrates lower EC50s considering chlorophyll fluorescence as an end-point; thus this parameter could be used as a biomarker in toxicity testing. Based on this study which elucidates the harm that this antifouling herbicide causes to S.japonica, one can surely ascertain that this weed killer and antifouling agent can also tremendously influence other marine communities too.