Ecotoxicological Assessment of Immersion Samples from Façade Render
To protect façade renders from growth of bacteria, fungi and algae, biocides can be added to a render before it is applied onto a façade. A comprehensive protection can be achieved by combining several biocides. During rain events and over time, biocides will gradually leach out and thus have the potential to affect soil or aquatic ecosystems. In this project the leaching behaviour of biocides from three render formulations was evaluated: one render containing free, another render containing encapsulated biocides (Terbutryn, OIT, DCOIT) and a control render without biocides. The renders were applied onto extruded polystyrene panels and water samples were generated over nine immersion cycles of the panels in accordance with standard EN 16105. Concentrations of the biocides were measured using LC-MS. The toxicity of the first and ninth immersion samples was determined using bioassays. Toxicity to aquatic organisms was evaluated by assessing inhibition of photosynthesis and algal growth rate, inhibition of bacterial luminescence and inhibition of daphnid population growth. Toxicity to soil organism was assessed by determining avoidance behaviour of worms and reproductive output in springtails. For aquatic effects, the toxic potential of a sample was expressed as a 50% effect concentration (EC50) based on sample dilution factors (DF; the sample volume and volume of culture medium used for dilution divided by the sample volume). Encapsulation reduced the leaching of Terbutryn, OIT, and DCOIT 4-, 17-, and 25-fold compared to free biocides used in the same amounts in the render. Generally, the toxicity of water from render containing encapsulated biocides was always lower than that of render with free biocides and toxicity was considerably lower for the ninth immersion day compared to the first immersion day sample for both free and encapsulated samples. Thus, on the first immersion day, the free biocide sample had a DF EC50 of 630, and the encapsulated biocides sample a DF EC50 of 130. On the ninth immersion cycle, the free biocide sample had a DF EC50 of 120 and encapsulated biocide sample a DF EC50 of 30. Toxicity therefore decreased 4- to 5-fold over the nine immersion cycles for both free and encapsulated samples. For the aquatic organisms, inhibition of photosynthesis was the most sensitive endpoint, followed by algal growth rate, bacterial bioluminescence and daphnid reproduction. At all tested sample concentrations, none of the samples with biocides caused effects on soil organisms. No toxicity was observed in control immersion samples without biocides in render although TOC (total organic carbon) reached up 250 mg/L. Results from bioassays matched quite well with expected bioassay responses based on chemical analysis and the toxicity of the individual biocides. It could be concluded, that the toxicity of given concentrations on algae is explained by Terbutryn whereas the toxicity on bacteria and daphnids is caused by DCOIT and OIT. The results thus indicated that other components in the render did not add to the toxicity of the individual biocides. Furthermore, the good agreement between the chemical analysis and the expected and observed biological effects indicates that the data are robust and that an assessment of the biological effect data using DF EC50 is a suitable evaluation tool for e.g. biocides released from treated articles or substances from construction products. Overall, the approach combining a standard leaching test with standard bioassays is very promising to evaluate the ecotoxicity of biocides leached out from façade renders.