Enzymes as useful biomarkers to assess the response of freshwater communities to pesticide exposure – A review

The lack of specificity of pesticides used for control of various organisms, even if efforts have been made to design formulations more species-specific, produce harmful effects on non-target organisms. Oxidative stress and lipid peroxidation are amongst the main known effects induced by pesticide exposure, besides eventual lethal toxicity, endangering organisms’ biomembranes integrity or compromising their activity through long-term exposure. Due to the general persistency of pesticides in the environment, these can easily be transported by water runoff. Pesticides used in agricultural fields are frequently transported to nearby freshwater systems, potentially affecting non-target organisms. Organophosphorus pesticides and carbamates are amongst the widely used classes of pesticides, and, despite being considered of rapid biodegradation, present a broad-spectrum of action, and the frequent transport of these contaminants to other systems may be harmful to non-intended species. Others, such as organochlorine pesticides, are highly persistent in the environment, posing a threat to non-target species for long periods. This is a matter of utter importance given that pesticides are known to impair numerous biological processes and inhibit the action of key enzymes in the response to xenobiotic-induced stress, potentiating oxidative stress and neurotoxicity, with potential irreversible effects. The study of the effect of pesticides has for long assessed exposure responses in a set of antioxidant and esterase enzymes, along trophic levels. The information is, however, more vast concerning photosynthetic organisms, macroinvertebrates and fish, with zooplankton appearing to be the group least studied. Given the ecological importance of zooplankton, further information regarding the response of this group to pesticide exposure could help detect early warning signs of potential threats to an ecosystem’s integrity and search for alternatives and solutions to prevent the harmful action of pesticides in non-target individuals, that escalate food chains. Nonetheless, the use of enzymes as biomarkers to assess the response of freshwater communities to stress induced by pesticides has for long proven to be an effective tool. Some constraints related to the consistency of organisms’ sensitivity and responses to pollutants may, however, lead to results not always straightforward, as a same pesticide may produce different enzymatic responses depending on the organism affected or to the environmental conditions. Thus, further studies using enzymes as biomarkers of pesticide exposure could provide more information and understanding to overcome the existing limitations and strengthen the applicability of enzymes in this context