Comparative responses of river biofilms at the community level to common organic solvent and herbicide exposure

Abstract

Residual pesticides applied to crops migrate from agricultural lands to surface and ground waters. River biofilms are the first aquatic non-target organisms which interact with pesticides. Therefore, ecotoxicological experiments were performed at laboratory scale under controlled conditions to investigate the community-level responses of river biofilms to a chloroacetanilide herbicide (alachlor) and organic solvent (methanol) exposure through the development referenced to control. Triplicate rotating annular bioreactors, inoculated with river water, were used to cultivate river biofilms under the influence of 1 and 10 μg L(-1) of alachlor and 25 mg L(-1) of methanol. For this purpose, functional (thymidine incorporation and carbon utilization spectra) and structural responses of microbial communities were assessed after 5 weeks of development. Structural aspects included biomass (chlorophyll a, confocal laser scanning microscopy) and composition (fluor-conjugated lectin binding, molecular fingerprinting, and diatom species composition). The addition of alachlor resulted in a significant reduction of bacterial biomass at 1 μg L(-1), whereas at 10 μg L(-1), it induced a significant reduction of exopolymer lectin binding, algal, bacterial, and cyanobacterial biomass. However, there were no changes in biofilm thickness or thymidine incorporation. No significant difference between the bacterial community structures of control and alachlor-treated biofilms was revealed by terminal restriction fragment length polymorphism (T-RFLP) analyses. However, the methanol-treated bacterial communities appeared different from control and alachlor-treated communities. Moreover, methanol treatment resulted in an increase of bacterial biomass and thymidine incorporation as well. Changes in dominant lectin binding suggested changes in the exopolymeric substances and community composition. Chlorophyll a and cyanobacterial biomass were also altered by methanol. This study suggested that the concentration-dependent effect of alachlor mainly remains limited to biomass and growth inhibition without apparent changes of structural and functional characteristics measured. Our work also establishes the potential toxic effects of organic solvents on river biofilm in ecotoxicological experiments. For the ecotoxicological experiments, the alternative of dissolution in organic solvent followed by its evaporation, depositing the chemical on a glass surface prior to dissolution in river water used here, appears to allow exposure while minimizing the effect of organic solvent.

An Assessment of the Toxicity of Pesticide Mixtures in Periphyton from Agricultural Streams to the Mayfly Neocloeon triangulifer

“…While pesticides entering surface waters may adsorb to periphyton, pesticides that do not partition into periphyton can also alter its nutritional value. This has been observed in cases where herbicide exposure has led to a decrease in periphyton biomass (Debenest et al, 2009; Paule et al, 2016), thereby limiting the food resources available to primary consumers. Pesticide exposure has also been shown to cause a shift in the composition of periphyton microorganisms toward species which are more tolerant of pesticide exposure (Schmitt‐Jansen & Altenburger, 2005).…”

Environmental microbiology as a mosaic of explored ecosystems and issues

“…Alachlor effect was mainly limited to biomass reduction only for younger biofilms (less than 2 weeks of age) without apparent changes in the ecological succession trajectories of bacterial and diatom communities and suggested that carbon utilization spectra of the biofilm are not damaged resulting. By using smaller triplicate rotating annular bioreactors, alachlor at 1 or 10 μg L −1 was applied through early stages of biofilm development, from time 0 to 5 weeks (Paule et al 2015). The results suggested that the concentration-dependent effect of alachlor mainly remains limitedto biomass andgrowth inhibition without apparent changes of ecological succession trajectories and functional characteristics.…”

Effects of the insecticide fipronil in freshwater model organisms and microbial and periphyton communities

“…This study showed that an insecticide such as fipronil may pose hazards to freshwater primary producers and decomposers. It has been demonstrated that herbicides (Paule et al, 2016;Chaumet et al, 2019;Dorigo et al, 2010) and their mixtures (Ham et al, 2014;Morin et al, 2012;Pesce et al, 2011) affect the microbial and photosynthetic fractions of the periphyton. However, as far as we know there is no information on the ecotoxicity effect of insecticides on biofilms.…”