Environmental Project, 977 – Survey of Estrogenic Activity in the Danish Aquatic Environment

Survey of Estrogenic Activity in the Danish Aquatic Environment

9 Conclusions

9.1 Sources of estrogens
     9.1.1 Wastewater treatment plants
     9.1.2 Sources in the open land
9.2 Estrogenic activity in the aquatic environment
     9.2.1 General state
     9.2.2 Streams receiving wastewater effluents
     9.2.3 Background locations
9.3 Types and forms of estrogens
     9.3.1 Contribution from the steroid estrogens
     9.3.2 Conjugated versus free estrogens
     9.3.3 Other chemicals may contribute to estrogenic activity
9.4 Geographical and seasonal variations
9.5 Environmental significance

9.1 Sources of estrogens

9.1.1 Wastewater treatment plants

At all sites and in nearly all samples from WWTPs estrogenic activity was found during the eight months duration of the sampling programme and some relatively clear relations between process technology and estrogenic activity in the effluent were noted.

It is clear that the modern WWTP with a de- and/or nitrification step releases very low concentrations of estrogens with the purified effluents. Also, the low tech treatment facilities i.e. reed beds and, in particular, biological sand filters demonstrate a promising capacity to retain estrogens.

The traditional, often relatively small WWTPs without nitrification and/or denitrification and only equipped with a trickling filter or even only a retention tank, are those with the poorest removal efficiency and therefore those who discharge the highest concentrations of estrogens with their effluents.

These treatment plants often serve very small rural communities and, thus, they can also be regarded as a kind of "open land sources". It is presently unknown if realistic technological solutions exist that can improve the performance of the small treatment plants with regard to estrogens.

9.1.2 Sources in the open land

The limited number of results from potential sources in the open land prevents firm conclusions to be drawn with regard to their relative share of the emissions of estrogens to the aquatic environment. However, the levels in septic tank effluents, which are typical of farms and other isolated houses in the countryside, were high, while the levels in the, albeit few, samples from other potential source types (drainage systems, fish farm effluents) in the open land were generally low.

Considering the few open land samples taken in this study and the huge amounts of manure (and to some extent sewage sludge) being applied to farmland in Denmark, the possible emissions to water courses with drainage water could deserve a closer examination. Such an examination should also include drains transporting septic tank effluents.

9.2 Estrogenic activity in the aquatic environment

9.2.1 General state

The data presented here for the general aquatic environment does not suggest a widespread occurrence of estrogenic activity at levels known to give feminisation of fish. In 33% of the samples from the aquatic environment (43 out of 130) the estrogenic activity if present was below the limit of detection (0.05 ng/L). However, low estrogenic activity is found with the YES assay in almost all types of freshwater environments in Denmark, but typically at concentrations lower than 1 ng/L. Only 25 out of the 130 samples had a level of total estrogenic activity higher than 1 ng/L (18 of these were below 2 ng/L), and the highest level observed in any sample was 8.8 ng/L.

9.2.2 Streams receiving wastewater effluents

In almost 70% of the water courses receiving effluents from WWTPs the level of estrogenic activity immediately downstream the discharge point (10 times the width of the water course) was higher than the upstream activity. In the remaining 30% the activity was either the same up- and downstream or the upstream activity was slightly higher.

When looking at samples taken further downstream the discharge point (approx. 100 times the width of the water course) the observed estrogenic activity was generally not any longer possible to relate to the wastewater discharges.

Hence, it may be concluded that in general the estrogenic activity provided by wastewater effluents is diluted or degraded to "general" levels within a relatively short distance from the discharge point. In the affected section of receiving water bodies the levels were often between 1-5 ng/L corresponding to 5-10 times the levels in background samples.

9.2.3 Background locations

In samples from the aquatic environment anticipated not to be influenced by human activities including those connected with husbandry, i.e. samples from "background" locations, the estrogenic level was non-detectable in 35% of the samples and in the rest it was low with weighted average of 0.1-0.4 ng/L. In particular the levels in background streams were low while some activity was detectable in a majority of the lake samples.

9.3 Types and forms of estrogens

9.3.1 Contribution from the steroid estrogens

Estrone is the steroid estrogen found most frequently and in the highest concentrations followed by estradiol. These two estrogens typically contribute with 80-100% of the sample activity from the analysed estrogens. In a few cases the indicator for husbandry (αE2) exceeds that of estradiol in WWTP samples, but does not rival estrone or estradiol in contribution to estrogenic activity due to low response factor in the YES assay. In the environmental samples αE2 is only occasionally found in significant concentrations, and is not attributable to expected cattle concentrations. Ethynylestradiol is only found rarely and in low concentrations, and in general the activity from ethynylestradiol is not a significant contribution to the total estrogenic activity neither in WWTP effluents nor in the aquatic environment.

9.3.2 Conjugated versus free estrogens

Estrogens are excreted from humans and animals mainly on a conjugated form while it is the free form that is active. The free form is ready to exhibit its estrogenic activity if released from WWTPs, but the conjugated form will only do so after loss of the conjugant (glucuronic acid or sulphate). During the transport in the sewerage system and in the subsequent WWTP processes the estrogens are bound or degraded, and the contribution of conjugated forms drops to 0-10% of the total activity in the effluent. In samples from the Danish aquatic environment and in the water courses receiving effluents almost all the activity (>90%) can be attributed to the free forms of estrogens. Thus, there is no "chemical time bomb" effect to be expected in the form of conjugated estrogens, which could cause a delayed effect in the aquatic environment.

9.3.3 Other chemicals may contribute to estrogenic activity

Estrogenic effects have been ascribed to natural and synthetic estrogens, xenoestrogens and phytoestrogens by scientists and regulatory bodies over the last decade. In some early studies xenoestrogens were responsible for dramatic effects, but now the contribution from natural and synthetic estrogens are considered to be the most important from an overall point of view. The present study shows that in a limited number of cases other substances than E1, E2 and EE2 probably contribute to the total estrogenic activity observed. However, because of the statistical uncertainty associated with the two methods it has not been possible to evaluate with certainty if or how much of the difference between the biologically detected and the chemically determined estrogenicity is due to an actual additional activity from other substances being present than E1, E2 and EE2.

9.4 Geographical and seasonal variations

Effluent samples taken during winter show lower estrogenic activity than summer samples at the measured sites. The difference between spring and fall samples does not suggest a general trend. Also the samples from the aquatic environment seem to exhibit more activity in the summer than in the winter.

It has not been possible to reveal any regional differences due to differences in soil types/geology, land use or demography in neither WWTP effluents, other sources or in the aquatic environment.

9.5 Environmental significance

The concentrations of estrogens present in the effluents from some of the WWTPs investigated in the present survey, in particular in the C and D categories, are obviously so high that they are likely to induce feminisation in male fish, whereas effluents from well-functioning WWTPs have contents of estrogens that probably are below an effect level. The estrogenicity levels in the surface water samples are generally lower than in the effluents, but with the existing scientific knowledge it cannot be excluded that feminisation can result from long term exposure to the levels observed in a number of the investigated streams and lakes.

The prediction whether or not estrogenic effects are likely to occur in a specific effluent or water body is, with our present knowledge, not straightforward. For example, Aerni et al. (2004) recently investigated WWTP effluents in Switzerland by means of both chemical analysis, the YES assay and analysis of vitellogenin in rainbow trout, and they found that some effluents induced vitellogenin production in the trout, but not in a way that was totally predictable from the YES-assay results or the results of the chemical analyses.

As previously mentioned the data presented here does not suggest a widespread environmental occurrence of estrogenic activity at levels known to give feminisation of fish. Nevertheless, it must be acknowledged that in water bodies heavily affected by WWTP effluents hormone disrupting effects have previously been found in fish. Given the levels of estrogenic activity in a number of effluents measured in this study, impacts may be observable at locations where an inefficient WWTP discharge a volume of effluent that is large compared to the flow in the receiving water course, e.g. in rural areas where creeks and small streams may receive a high proportion of effluents from less advanced WWTPs.