Effects of insecticide Profenofos and herbicide MCPA on leaf litter decomposition in tropical streams: a microcosm study

Agricultural pesticides are known to significantly impact the non-target aquatic communities and key ecosystem processes of stream ecosystems such as litter decomposition. The unresolved questions are remaining of how such stressors interact to alter ecosystem structure and function, and how impacted ecosystems are able to maintain their ecological balance. Hence, this paper discusses the effects of the insecticide Profenofos and herbicide MCPA on Ficus racemosa and Panicum maximum litter breakdown in 40 days of indoor microcosm systems. Litter breakdown rates were analysed in microcosms treated with pesticide concentrations of 0.010, 0.025, 0.100, 0.250, 1.000 mg/L and in control tanks with no pesticides. The results of the study indicated a significant alteration of litter breakdown rate of MCPA-treated tanks compared to the control tanks in terms of reduction percentage of dry weight, remaining organic matter content, microbial community sporulation, and remaining nutrient content ( p < 0.05). The herbicide MCPA accelerated the structural impairment of leaf material by destructing the leaf material. No significant differences were observed between Profenofos-treated leaf packs and control leaf packs ( p < 0.05). Aquatic hyphomycetes have degraded the applied Profenofos by consuming the nutrients from the litter. These alterations were modulated by the litter quality and microbial colonizations on leaf materials. The findings of the study emphasize the effects of pesticides on the structure and functional properties of lower levels organisms in the ecological food chain and the importance of considering indirect effects of pesticides in ecological processes.