Effects of the agricultural pesticides atrazine, deethylatrazine, endosulfan, and chlorpyrifos on an estuarine microbial food web

Abstract

Aricultural pesticide runoff is a critical issue for many southeasternestuaries. The estuarine microbial food web plays an important role in nutrient cycling and transfer of nutrients to higher trophic levels. The present study examined the effects of agricultural pesticides on the estuarine microbial food web. Polyurethane foam substrates were used to collect microbial communities from a reference tidal creek in the North Inlet National Estuarine Research Reserve (Georgetown, SC, USA). Colonized substrates were brought into the laboratory and exposed to the following commonly used agricultural pesticides: atrazine (and a metabolite, deethylatrazine), endosulfan, and chlorpyrifos. Chlorophyll a, phototrophic carbon assimilation, dissolved oxygen, and phototrophic biovolume were significantly reduced at concentrations of 50 and 250 μg/L atrazine and deethylatrazine. Generally, inhibition of the phytoplankton resulted in increased bacterial abundance and productivity, whereas heterotrophic ciliate and flagellate abundances were not affected. Total bacterial abundance, but not heterotrophic bacterial productivity, was significantly reduced with endosulfan treatments of 1 and 10 μg/L. Endosulfan was primarily found to target the cyanobacteria. Changes in biomass reflected compositional shifts in the phototrophs. The abundance of heterotrophic ciliates and flagellates was significantly reduced at 10 μg/L chlorpyrifos. Bacterial abundance and productivity increased, whereas phototrophic variables decreased. Agricultural pesticides were found to alter both functional and structural aspects of the estuarine microbial food web.

Effects of Endosulfan (Thiodan 35 EC®) on Meiofauna Community Through a Microcosm Approach

“…Although kinorhynchs present their bodies covered by a strongly water-repelling cuticle (Giere, 2009), a fact that favors the passive uptake of pesticides, this group showed of the endosulfan applied through the Thiodan pesticide may have been degraded to endosulfan sulfate (unmeasured values). Both endosulfan isomers exhibited relatively short half-lives and the present results are consistent with other microcosm studies that reported significant losses of more than 50% in two weeks or even during the first days after the application of initial nominal concentrations (Guerin & Kennedy, 1992;Berrill et al 1998;DeLorenzo et al 1999). In addition, according to Laabs et al (2007), small microscosm systems ( < 1 L) have a low surface/volume ratio that favors endosulfan hydrolysis and losses by edge effects, fact also observed previously in the studies of Flemer et al (1995) and Barry & Logan (1998).…”

Agricultural pesticides and selected degradation products in five tidal regions and the main stem of Chesapeake Bay, USA

“…An assessment of ecological risk from atrazine and metolachlor in Chesapeake Bay streams and tributaries found that these chemicals did not pose a significant risk [12]. However, other studies have found that agricultural herbicides and insecticides alter the function of estuarine microbial food webs [13,14]. High concentrations of atrazine were found to inhibit the growth of an important marsh plant, Juncus roemeriannus [15].…”

Do persistent organic pollutants stimulate cyanobacterial blooms?

“…Although pesticides (i.e., insecticides) and fungicides have been found to favor cyanobacteria over other phytoplankton taxa in laboratory studies (Wendt-Rasch et al 2003, Ma et al 2008, other mesocosm and laboratory studies have shown mixed results ( Fig. 2; DeLorenzo et al 1999, Leboulanger et al 2011. In natural systems, heterotrophic bacteria, zooplankton, and fungi community composition may play a role in the success of cyanobacteria in the presence of POPs compared to other phytoplankton.…”

“…They concluded that cyanobacteria were more tolerant to atrazine than other phytoplankton taxa, particularly under conditions of elevated nutrient supply. Other studies have found that cyanobacteria and/ or diatoms are more tolerant to atrazine than chlorophyte phytoplankton taxa (DeLorenzo et al 1999, Magnusson et al 2012), suggesting that in cyanobacteriachlorophyte co-dominated systems, the presence of herbicides like atrazine may have the potential to shift the system to cyanobacterial dominance. Additionally, although most relevant studies in our meta-analysis held nutrient concentrations and temperature constant when comparing cyanobacteria and eukaryotic phytoplankton taxa in the presence of POPs, Bérard et al (1999) reported that inhibition of cyanobacterial growth by herbicides is reduced at elevated water temperatures, and we thus have concerns that global warming could potentially influence or modify interactions between eutrophication and POP stressors.…”