Fate and Effects of Triclosan

Fate and Effects of Triclosan

5 Discussion and conclusions

As there is almost no information available on concentrations of Triclosan in Danish waste water, WWTPs or sewage sludge, the assessments were based on information from other countries.

The available studies regarding the fate of Triclosan in WWTPs showed that Triclosan is degradable under aerobic conditions in WWTPs and that the substance is extensively degraded and removed in activated sludge systems. Furthermore, Triclosan does not seem to affect the treatment processes at levels up to 2 mg/L in the influent. However, the available information indicates that only little or no removal of Triclosan occurs during anaerobic sludge digestion.

Apart from microorganisms (which Triclosan is designed to inhibit), the group of organisms most sensitive to Triclosan is plants (algae and cucumber). It must be stressed that the available data on effects of Triclosan on aquatic and soil-living organisms are very limited – especially for the soil compartment.

Therefore, the risk assessments had to be based on very cautious assumptions and, consequently, they are very conservative.

Based on conservative assumptions regarding dilution of the waste water (water courses with low flow and a dilution factor of 2-10), PEC values were derived from Triclosan concentrations in U.S., Swedish and Swiss waste water. The resulting PEC/PNEC ratios (risk quotients, RQ) for surface water were > 1 for low technology WWTPs (RQ = 3-25) and for part of the modern plants, because the RQ range was between 0.2 and 6.

In Denmark, only small local Danish WWTPs may however produce effluents and sewage sludge attaining the level of the foreign lower technology plants and, for most waste water discharges from Danish WWTPs, the dilution will be considerably higher than 10. Therefore, Triclosan is not expected to cause effects in Danish surface water unless discharges are from low technology plants to waters with low dilution.

Based on a preliminary PNEC value and measurements in U.S. and Swedish sludge, the majority of the risk quotients for the soil compartment are > 1. Except for the sample with the lowest concentration of Triclosan, all the concentrations of Triclosan in sludge measured in U.S. and Swedish samples would thus be expected to cause effects in the soil immediately after application of the maximum amount used in Denmark.

For a more realistic terrestrial risk assessment, information regarding concentrations of Triclosan in Danish sewage sludge would be needed. Furthermore, toxicity data of high quality for terrestrial organisms would improve the reliability of the PNEC value.

The outcome of the risk assessments for surface water and soil cannot be considered conclusive for Danish conditions. Based on information on Danish WWTPs, it is, however, considered likely that most Danish effluent waste water and most Danish sewage sludge will contain concentrations of Triclosan at the level of the low values measured in Sweden, Schwitzerland and the U.S.A.. Only at small local WWTPs, effluents and sewage sludge are expected to attain the level of the foreign lower technology plants.

The very sparse information on Danish conditions indicates that, for aquatic environments, risk quotients below 1 may be obtained for discharges for most WWTPs. This is expected for effluents from high technology WWTPs with a high dilution in the recipient. However, discharge of waste water to watercourses with very low flow may lead to risks of effects. For verification, results of analysis could be used, only if measurements are made with low detection limits. For terrestrial environments, there is no information regarding concentrations of Triclosan in Danish sewage sludge.