A synthesis of the effects of pesticides on microbial persistence in aquatic ecosystems

Abstract

Pesticides are a pervasive presence in aquatic ecosystems throughout the world. While pesticides are intended to control fungi, insects, and other pests, their mechanisms of action are often not specific enough to prevent unintended effects, such as on non-target microbial populations. Microorganisms, including algae and cyanobacteria, protozoa, aquatic fungi, and bacteria, form the basis of many food webs and are responsible for crucial aspects of biogeochemical cycling; therefore, the potential for pesticides to alter microbial community structures must be understood to preserve ecosystem services. This review examines studies that focused on direct population-level effects and indirect community-level effects of pesticides on microorganisms. Generally, insecticides, herbicides, and fungicides were found to have adverse direct effects on algal and fungal species. Insecticides and fungicides also had deleterious direct effects in the majority of studies examining protozoa species, although herbicides were found to have inconsistent direct effects on protozoans. Our synthesis revealed mixed or no direct effects on bacterial species among all pesticide categories, with results highly dependent on the target species, chemical, and concentration used in the study. Examination of community-level, indirect effects revealed that all pesticide categories had a tendency to reduce higher trophic levels, thereby diminishing top-down pressures and favoring lower trophic levels. Often, indirect effects exerted greater influence than direct effects. However, few studies have been conducted to specifically address community-level effects of pesticides on microorganisms and further research is necessary to better understand and predict the net effects of pesticides on ecosystem health.

Do host‐associated gut microbiota mediate the effect of an herbicide on disease risk in frogs?

“…In contrast, many contaminants can be directly toxic to microbiota (Fig. 1 path c ) (Staley et al 2015). In hosts, exposure to pollutants, especially during formative stages of life, can induce immediate and lasting changes to gut bacterial communities (Fig.…”

“…paths c-e, g-a-b, a-f-e) (Claus, Guillou, & Ellero-Simatos, 2016). Many microbes are instrumental in breaking down pollutants in the environment ( Figure 1, path g) (Bansal, 2012;Häggblom, 1992;Horvath, 1972;Staley, Harwood, & Rohr, 2015) and thus the contaminants can serve as a resource for microbiota, potentially increasing some of their abundances. In contrast, many contaminants can be directly toxic to microbiota (Figure 1 path c) (Staley et al, 2015).…”

“…Many microbes are instrumental in breaking down pollutants in the environment ( Figure 1, path g) (Bansal, 2012;Häggblom, 1992;Horvath, 1972;Staley, Harwood, & Rohr, 2015) and thus the contaminants can serve as a resource for microbiota, potentially increasing some of their abundances. In contrast, many contaminants can be directly toxic to microbiota (Figure 1 path c) (Staley et al, 2015). In hosts, exposure to pollutants, especially during formative stages of life, can induce immediate and lasting changes to gut bacterial communities (Figure 1, path c) (Kohl, Cary, Karasov, & Dearing, 2015;Shehata, Schrödl, Aldin, Hafez, & Krüger, 2013).…”

Atrazine and amphibians: Data re-analysis and a summary of the controversy

“…The documented positive relationship between biodiversity and ecosystem functions and services, such as pest and disease control, primary production, and clean water (Dobson et al 2006, McMahon et al 2012, Staley et al 2014, Venesky et al 2014a, Civitello et al 2015, Cohen et al 2016, De Laender et al 2016) and the importance of indirect effects of chemicals mediated by species interactions (Rohr et al 2006a, Clements and Rohr 2009, Halstead et al 2014, Douglas et al 2015, Staley et al 2015) has prompted several researchers to study the effects of atrazine on freshwater communities containing amphibians rather than on isolated amphibian species (de Noyelles et al 1989, Boone and James 2003, Rohr and Crumrine 2005, Rohr et al 2008c, Halstead et al 2014). Many of these studies report alterations of amphibian growth and abundance that seem to be caused by atrazine•induced changes in photosynthetic organisms.…”

Effects of a larval mosquito biopesticide and Culex larvae on a freshwater nanophytoplankton (Selenastrum capricornatum ) under axenic conditions

“…Alternatively, pesticides may directly impact autotrophic microbial communities in aquatic ecosystems (e.g., Wurtsbaugh and Apperson , Widenfalk et al , , Staley et al ). For instance, high doses of pesticides such as methoprene, temephos, dimilin, propoxur, and methoxychlor were shown to influence algal growth accompanied by increased nitrification (Wurtsbaugh and Apperson ).…”