Developmental effects of zebrafish (Danio rerio) embryos after exposure to glyphosate and lead mixtures

Natural aquatic environments have a heterogeneous composition; therefore, simultaneous exposure to multiple contaminants is relevant and more realistic when assessing exposure and toxicity. This study examines the combinatorial effects of two compounds found ubiquitously in drinking water across the United States: glyphosate and lead acetate. Zebrafish (Danio rerio) embryos were used as a model for investigating developmental delays following controlled exposures. Six different environmentally relevant exposure concentrations of glyphosate, ranging from 0.001 to 10 ppm, and lead acetate, ranging from 0.5 to 4 ppm, were applied first as single exposures and then as co-exposures. The sublethal endpoints of hatching and coagulation were quantified to determine potencies. Results indicate that higher concentrations of the individual chemicals correlate with later hatching with correlation coefficients of 0.71 and 0.40 for glyphosate and lead acetate respectively, while the co-exposure at lower concentrations induced earlier hatching with a correlation coefficient 0.74. In addition, increased levels of coagulation and glutathione reductase activity were observed following co-exposure, as compared to the individual exposures, suggesting potential toxicological interactions. These results support the need for further work assessing the combined potencies of aquatic contaminants rather than individual exposures.

Snail bioaccumulation of triclocarban, triclosan, and methyltriclosan in a North Texas, USA, stream affected by wastewater treatment plant runoff

Grazing by freshwater snails promotes nutrient turnover in algal communities. Grazed algal compartments may include antimicrobial agents and metabolites, such as triclocarban (TCC), triclosan (TCS), and methyltriclosan (MTCS), which are incompletely removed by wastewater treatment plant (WWTP) processing. The present study quantifies snail bioaccumulation factors (BAFs) for TCC, TCS, and MTCS at the outfall of Pecan Creek (TX, USA), the receiving stream for the city of Denton (TX, USA) WWTP. Helisoma trivolvis (Say) is ubiquitous and thrives under standard laboratory conditions, leading to its choice for this bioaccumulation study in conjunction with Cladophora spp. Along with providing substrate for epiphytic growth, Cladophora spp. provide a source of food and shelter for H. trivolvis. After being caged for two weeks, algae and snails were collected from the WWTP outfall, along with water-column samples, and analyzed by isotope dilution gas chromatography-mass spectrometry for TCS and MTCS and by liquid chromatography-mass spectrometry for TCC. Algal and snail samples were analyzed before exposure and found to be below practical quantitation limits for all antimicrobial agents. Triclocarban, TCS, and MTCS in water samples were at low-ppt concentrations (40-200 ng/L). Triclocarban, TCS, and MTCS were elevated to low-ppb concentrations (50-300 ng/g fresh wt) in caged snail samples and elevated to low-ppb concentrations (50-400 ng/g fresh wt) in caged algal samples. Resulting snail and algal BAFs were approximately three orders of magnitude, which supports rapid bioaccumulation among algae and adult caged snails at this receiving stream outfall. The results further support TCC, TCS, and MTCS as good candidate marker compounds for evaluation of environmental distribution of trace WWTP contaminants.

Algal bioaccumulation of triclocarban, triclosan, and methyl-triclosan in a North Texas wastewater treatment plant receiving stream

Algae comprise the greatest abundance of plant biomass in aquatic environments and are a logical choice for aquatic toxicological studies, yet have been underutilized in this capacity. The lipid content of many algal species provides a point of entry for trophic transfer of lipophilic organic contaminants. Triclosan (TCS) and triclocarban (TCC), widely used antimicrobial agents found in numerous consumer products, are incompletely removed by wastewater treatment plant (WWTP) processing. Methyl-triclosan (M-TCS) is a metabolite of TCS more lipophilic than the parent compound. The focus of this study was to quantify algal bioaccumulation factors (BAFs) for TCS, M-TCS, and TCC in Pecan Creek, the receiving stream for the City of Denton, Texas WWTP. The complex algal compartment was field identified for collection and verified by laboratory microscopic description as being comprised of mostly filamentous algae (Cladophora spp.) and varying inconsequential levels of epiphytic diatoms and biofilm. Algae and water column samples were collected from the WWTP outfall, an upstream site, and two downstream sites and analysed by isotope dilution gas chromatography/mass spectrometry (GC/MS) for TCS and M-TCS and liquid chromatography/mass spectrometry (LC/MS) for TCC. TCS, M-TCS, and TCC in Pecan Creek water samples taken at and downstream from the WWTP were at low ppt concentrations of 50-200 ng l(-1) and were elevated to low ppb concentrations of 50-400 ng g(-1) fresh weight in algae collected from these stations. The resulting BAFs were approximately three orders of magnitude. TCS, M-TCS and TCC appear to be good candidate marker compounds for evaluation of environmental distribution of trace WWTP contaminants. Residue analysis of filamentous algal species typically occurring in receiving streams below WWTP discharges is a readily obtained indicator of the relative bioaccumulative potential of these trace contaminants.