Laboratory-based experiments to investigate the impact of glyphosate-containing herbicide on pollution attenuation and biodegradation in a model pervious paving system

An experimental investigation was carried out to determine the effect of glyphosate-containing herbicides (GCHs) on the hydrocarbon retention and biodegradation processes known to occur in pervious pavement systems (PPSs). The PPS test rigs were based on the four-layered design detailed in CIRIA C582. This enabled the pollutant retention capacity of the PPS and biodegradation of retained pollutants by microorganisms to be investigated. The use of test rigs also enabled the impact of GCH on PPS eukaryotic organisms to be studied, by the monitoring of protist bioindicators. Results showed that GCH disrupted hydrocarbon retention by the geotextiles relative to rigs with mineral oil only added, as 9.3% and 24.5% of added hydrocarbon were found in herbicide only rigs and herbicide plus oil rigs respectively. In previous studies, PPS contaminated by mineral oil had been shown to retain 98.7% of added oils and over several weeks, biodegrade this oil in situ. Where GCH was added to experimental models, much higher concentrations of heavy metals, including Pb, Cu, and Zn, were released from the PPS in effluent, particularly where GCH and mineral oil were added together. The source of the majority of the metal contamination was thought to be the used engine oil. The herbicide generally increased the total activity of microbial communities in rig systems and had a stimulating effect on bacterial and fungal population numbers. Although the protists, which are part of the microbial community directly or indirectly responsible for biodegradation, were initially strongly affected by the herbicide, they showed resilience by quickly recovering and increasing their population compared with rigs without added herbicide, including the rigs with mineral oil added to them. However, the presence of herbicide was associated with a decrease in the species richness of recorded protist taxa and a predominance of robust, cosmopolitan or ubiquitous protist genera.