Development of Aquatic Quality Standards (QSs) for Dioxins

July 2003

Executive Summary

This report summarises the findings of a project to review literature and to derive quality standards for dioxins in the aquatic environment using two methodologies: the UK method used previously to derive Environmental Quality Standards for the UK, and the proposed EC method developed by the Fraunhofer Institute. Data on toxicity, bioaccumulation and biomagnification of dioxins in the aquatic environment were collated and quality checked, prior to use in the derivation of standards for the protection of freshwater and marine life and human health. The UK method derives standards only for freshwater, marine waters and abstraction of drinking water, while the proposed EC methodology includes aspects of secondary poisoning to higher life forms and dietary exposure in humans.

UK standards have been derived for individual congeners (the seven 2,3,7,8-chlorine substituted congeners) using a combination of available data and relative potencies based on the most toxic, i.e. 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). Owing to a lack of data on toxicity, bioconcentration and biomagnification factors, quality standards could only be derived for 2,3,7,8-TCDD using the EC method.

The two methodologies used to derive the quality standards are compared and their advantages and disadvantages discussed. Because of the physico-chemical and toxicity attributes of dioxins, a careful and pragmatic approach is required in order to set environmental quality standards that are meaningful and practical. The exceedingly high potential for dioxins to sorb to organic matter means that only a minute proportion of their total concentration exists purely in the dissolved phase. Setting standards on this basis may lead to values in excess of their solubility, less than analytical limits of detection or below background levels. Exposure concentrations of dioxins are also extremely low, and as a result acute effects are almost never seen in the environment. Setting standards for acute exposure is therefore not relevant. Most toxic effects are observed higher up the food chain, which means that most dioxin standards should be based upon protecting these organisms (typically fish, wild mammals and humans), rather than freshwater and marine invertebrates and algae. However, deriving standards to protect more sensitive higher life forms may lead to over-protection of the aquatic environment, which may require discussion at regulatory levels.

A summary of the derived quality standards is presented in Table 1.1.

Table 1.1 Comparison of UK and EC quality standards for 2,3,7,8-TCDD
Protection Objective UK Method EC Method
Pelagic community (freshwater) 0.01 ng l-1
(aquatic toxicity threshold)
0.0011 ng l-1
corresponding conc. in SPM: 60 ng kg-1 dry wt
Pelagic community (saltwater) Not applicable No data available with which to set standard
Benthic community (freshwater sediment) 55 ng kg-1
(for 3% OC)
185 ng kg-1
(for 10% OC)
75 ng kg-1
wet wt(345 ng kg-1 dry wt)
Benthic community (marine sediment) 55 ng kg-1
(for 3% OC)
No data available with which to set standard
Predators (secondary poisoning) Not applicable QSsecpois.biota = 0.73 µg kg-1 prey (biota tissue wet wt)
corresponding QSsecpois.water = 0.4 pg l-1 in the best case (however, the derivation of reliable corresponding QSsecpois.water is not possible with available data on bioaccumulation)
Food uptake by man Not applicable 0.12 ng kg-1 food (seafood) translated to at of 0.006 pg l-1 using a BCF for fish of 20,000
Drinking water abstraction Derivation of QS not required 0.007 ng l-1

Copies of this report may be available as an Acrobat pdf download under the 'Completed Research' heading of the Research Page on the DWI website.