Fate and Effects of Triclosan

Fate and Effects of Triclosan

Summary

Studies regarding the fate and effects of Triclosan were reviewed in order to describe the fate of Triclosan in wastewater treatment plants (WWTPs) and to make environmental risk assessments of Triclosan.

The reviewed studies (made available by the Danish EPA) showed that Triclosan is degradable under aerobic conditions in WWTPs and is extensively degraded and removed in activated-sludge systems. Furthermore, Triclosan does not adversely impact the treatment processes at levels up to 2 mg/L in the influent. However, monitoring studies indicate that only little or no removal of Triclosan occurs during anaerobic sludge digestion. Monitoring of Triclosan concentrations at WWTPs in the U.S.A., Sweden, Switzerland and Denmark showed the following ranges of Triclosan concentrations:

· Influent: 0.1-16.6 µg/L
· Effluent: 0.10-2.70 µg/L
· Sludge: 0.028-15.6 µg/g (dry weight)

Studies regarding photolysis of Triclosan in surface water have demonstrated that this may be a significant pathway in the upper layers of lakes. E.g. at pH 8, 4.6% of the parent compound was transformed to the dioxin 2,8-DCDD. Such a transformation can, however, only be expected in the upper layers of lakes due to sorption of light in the water column. Therefore, dioxin concentrations in the entire water column are expected to be lower. 2,8-DCDD does not have “the dioxin effect" and the WHO has not assigned any dioxin toxicity equivalent to it.

The estimates of Predicted Environmental Concentrations (PEC) were based on information regarding U.S., Swedish and Swiss conditions. Conservative estimates of PEC values of Triclosan in surface water were calculated by application of the principles used in the EU and those of the Danish EPA. A potential background concentration of Triclosan was not included in the PEC_{surface water} . The resulting ranges of PEC values were:

PEC_{surface water} : 0.009-0.303 µg/L for high technology plants
PEC_{surface water} : 0.149-1.26 µg/L for low technology plants

The lowest NOEC value for aquatic organisms was a NOEC for algae of 0.5 µg/L. Based on the EU principles for derivation of Predicted No Effect Concentrations (PNEC), the resulting PNEC value was

^PNECsurface water^{= 0.05 µg/L}

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 most of the high technology plants (RQ = 0.2-6).

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 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.

From Danish WWTPs, only one measurement of the Triclosan concentration in the effluent from a WWTP is available and it was below the limit of detection (1 µg/L).

For the soil compartment, the PEC estimate was based on information on concentrations of Triclosan in U.S. and Swedish sewage sludge. For realistic worst-case application rates, the Danish application scheme for sewage sludge was used. The resulting PEC values for the soil compartment were:

Activated sludge: PEC_soil = 0.00004-0.0056 mg/kg (soil dry weight)
“Bio-filter” sludge:PEC_soil= 0.0005-0.021 mg/kg (soil dry weight)

The only soil-living organisms, which have been tested with Triclosan, are plants and worms, of which plants are the most sensitive species. Based on the lowest available NOEC value and the principles used in the EU, a preliminary PNEC was estimated to be:

PNEC_soil = 0.096 µg/kg (soil dry weight)

The terrestrial risk assessment indicated risks of adverse effects on soil-living organisms following application of most of the sewage sludge to agricultural soil. Risk quotients ranged between 0.4 and 219. The lowest value was based on the lowest concentration found in activated sludge from Sweden while the highest was derived from a U.S. trickling filter plant.

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.

Due to lack of data on Danish conditions, all information regarding concentrations of Triclosan in waste water, effluents and sewage sludge was from the U.S.A., Sweden or Switzerland. Therefore, 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 lowest 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.