Potential microbial toxicity and non-target impact of different concentrations of glyphosate-containing herbicide (GCH) in a model pervious paving system

Pervious Pavement Systems are Sustainable Drainage devices that meet the three-fold SUDS functions of stormwater quantity reduction, quality improvement and amenity benefits. This paper reports on a study to determine the impact of different concentrations of glyphosate-containing herbicides on non-target microorganisms and on the pollutant retention performance of PPS. The experiment was conducted using 0.0484 m(2) test rigs based on a four-layered design. Previous studies have shown that PPS can trap up to 98.7% of applied hydrocarbons, but results of this study show that application of glyphosate-containing herbicides affected this capability as 15%, 9% and 5% of added hydrocarbons were released by high (7200 mg L(-1)), medium (720 mg L(-1)) and low (72 mg L(-1)) glyphosate-containing herbicides concentrations respectively. The concentrations of nutrients released also indicate a potential for eutrophication if these effluents were to infiltrate into aquifers or be released into surface waters. The effect of glyphosate-containing herbicides application on the bacterial and fungal communities was slightly different; fungi exhibited a "top-down" trend as doses of 7200 mg L(-1) glyphosate-containing herbicides yielded the highest fungal growth whilst those with a concentration of 720 mg L(-1) glyphosate-containing herbicides applied yielded the highest bacterial growth. In the case of protists, doses of glyphosate-containing herbicides above 72 mg L(-1) were fatal, but they survived at the lower concentration, especially the ciliates Colpoda cucullus and Colpoda steinii thus indicating potential for their use as biomarkers of herbicide-polluted environments. Data also showed that at the lowest concentration of glyphosate-containing herbicides (72 mg L(-1)), biodegradation processes may not be affected as all trophic levels required for optimum biodegradation of contaminants were present.