Response of microbial organisms (aquatic and terrestrial) to pesticides

Abstract

A systematic literature search was carried out in order to assess the response of microbial organisms to pesticides in aquatic and terrestrial environments. The major literature databases have been interrogated, and after a refinement of keywords, thousands of records were retrieved and manually screened for relevance, quality, publication date, language and suitability for quantitative metaanalyses. 234 records for the terrestrial lot and 42 records for the aquatic lot were retained after screening and analysed for the extraction of several relevant information regarding the type of study, the pesticide application dose, the microbial parameters measured. From each record, a number of case studies were extracted, a case study being represented by the measurement of a single product, at a specific dose on a specific microbiological endpoint. A high number of case studies (3405 for terrestrial and 458 for aquatic) were obtained, stored and analysed through an Access database query system. With such a query system, it was possible to show on a detailed semi-quantitative way that pesticides affect microbes in a number of ways, with significant reductions in microbiological endpoints of biomass and activity detected in less than half of the cases considered. Furthermore, a number of temporary effects were identified, with microbial endpoints being firstly affected and then restored to the original conditions. This report confirms on one hand the complexity of microbial parameters in terrestrial and aquatic environments, on the other the importance of considering carefully microbial features in the risk assessment of pesticides. In this context, the adoption of a macro-categorization of microbial responses (biomass, activity and structure) can be useful for handling complex data and to identify patterns that can be potentially used for the goal of protecting microorganisms from potential adverse effects of pesticides. Carrying out risk assessment for nontarget microbes on single molecules, as usually done for the risk assessment of pesticides, will be very important in order to identify which ones are eventually causing more detrimental effects. The literature survey also indicated that the pesticide applied dose strongly affect the outcomes, with less impacts when the pesticides are being applied at recommended field doses: it is thus recommended to further promote policies for use of pesticides according to good agricultural practices, since this can reduce side-effects on non-target soil microorganisms.