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Survey of Estrogenic Activity in the Danish Aquatic Environment Part B
5 Conclusions
5.1 Simple WWTPs
There appears to be some discrepancy between the findings in Part A and Part B of the survey regarding the estrogenic activity in the effluents from Category C WWTPs. However, also in Part A there was
a quite significant variation among the results within this category. It is, though, still the overall impression that the small mechanical and mechanical-biological WWTPs generally are not very effective with
regard to elimination or reduction of steroid estrogens.
The number of category C plants in Denmark appears to be decreasing, from 336 in 2001 to 277 in 2004, while the number of category D plants has almost remained unchanged over the same period
(DEPA 2002, 2003, 2004, 2005b).
The technical possibilities for improvement of the performance of the small mechanical and mechanical-biological treatment plants can typically include the following items in prioritised order:
- General optimisation of treatment plant operation by improved monitoring and control sludge concentration in the process tank, oxygen supply and discharge of suspended solids.
- Increase of sludge age and hydraulic retention time in the process tank. This could have the environmental side-effect that the plant is upgraded from MB plant to MBN plant.
- Improve the performance of secondary clarifier by installation of lamella separators, Flockbee or similar or by construction of additional secondary clarifier volume.
- Installation of polishing unit (conventional sand filter, biological sand filter or lagoons.
The best technical-economical solution for the individual treatment plants should be based on an individual assessment. Shutting down of the small treatment plant and pumping of wastewater to a central
WWTP can for some plants be the best technical-economical solution.
5.2 Septic tank effluents
Septic tank effluents generally contain steroid estrogens at levels requiring 10-100 times dilution (or more) before being brought down to concentration levels below biological effect levels. More than half of
the septic tanks in the open land in Denmark discharge into field drains from which only half of the volume is estimated to reach surface waters while the rest seeps out of the drains and into the soil where the
estrogens will be degraded if/when aerobic conditions prevail.
Several thousands septic tank systems are in operation on properties in the Danish countryside. In DEPA's annual "Point source report" for 2004 (DEPA 2005b) the number of septic tanks discharging
directly or via field drains is reported to be around 51.000 and 89.000, respectively (DEPA, 2005b). The majority of these, 41.000 and 66.000, respectively, are associated with single houses/farms while
the remaining are properties in either villages or in recreational areas (summer cottages).
The majority of the municipalities had by the end of 2004 agreed on local sanitation plans, which should ensure improved treatment at 59% of the 96.000 properties for which improved treatment is required
in the regional physical planning (DEPA 2005b). The majority of the plans are expected to be implemented before 2010 and, thus, the number of systems discharging directly or via drains into the freshwater
environment is expected to decrease significantly in the coming years.
5.3 Field drains
Within the framework of this survey (Part A and B) it has only been possible to carry out a rather limited investigation of the possible contamination of the aquatic environment by discharges of water from
field drains, which are widespread in many Danish agricultural areas. The duration of the monitoring was up to three weeks per location, but in reality continuous monitoring covering at least a full hydrological
cycle (i.e. at least one year) is necessary before firm conclusions can be drawn. Further, a wider range of agricultural soil types should be studied.
The limited monitoring that was carried out in this study did, however, only reveal presence of low or undetectable estrogenic activity in drainage water from fields where liquid manure or sewage sludge was
applied to the soil shortly prior to the sampling.
Further, the monitoring of surface water from streams and small lakes in husbandry areas in Part A of the survey showed that the levels were mostly below or around 1 ng E2 equiv./L and only in one case
did the level in a stream exceed 5 ng E2 equiv./L. The latter result could not be confirmed by the chemical analysis of the same sample.
5.4 Impact of discharges on small streams
5.4.1 Impact on water quality
The survey (Part A and B) has demonstrated that low levels of estrogenic activity occur in streams where discharge of treated effluents from Cat. C/D WWTPs take place. However, only at one out of a
total of 18 WWTPs where up- and downstream samples were taken did the activity level increase significantly as a result of the effluent discharge. In all other cases the level remained within the "normal"
range observed in streams i.e. from the sub-ng E2 equiv./L level to the 3 ng E2 equiv./L level.
Thus, it has not in this study been possible to demonstrate that even significant estrogenic activity levels in sewage effluents should generally lead to levels in the freshwater environment where significant
biological effects are known to occur.
However, also other sources such as field drains and septic tank effluents contribute to the overall load on the small streams in arable areas. The largest volume of water from these two types of
contamination sources stems from the discharges of drainage water from fields. In some parts of Denmark a significant fraction (even the majority) of the fields are fertilised with pig or cattle manure while the
application of sewage sludge only takes place on a rather limited fraction of the total agricultural area in Denmark. However, only low (sub-ng) levels or even no estrogenic activity could be detected in field
drain water samples in this investigation.
In contrast to this, septic tank effluents generally show significant estrogenic activity i.e. levels some 10-100 times (or more) higher than levels where biological effects have been observed. The volume of
these effluents reaching the streams will, however, in most cases be small compared to the flow in the streams though the existence of local "hot spots" is possible.
In the survey of streams and rivers of varying size in Part A (and the few samples in Part B) of the survey, the levels of estrogenic activity was generally at the sub-ng - 1 ng E2 equiv./L and did only in a few
cases exceed a level of 3 ng E2 equiv./L. In England, the NOEC of estrogenic activity is presently considered to be 1 ng E2 equiv./L but this value may be subject to revision.
5.4.2 Impact on sediment quality
All sediments demonstrated significant contents of steroid estrogens when analysed chemically and about half of the samples also gave a response in the biological assay. The results demonstrate that despite
the absence of activity in the water samples, the WWTPs obviously release estrogens that, due to their lipofilicity when appearing on the free form, tend to sorb to particulates (organic matter) and precipitate
in sedimentation sections of the streams.
The analyses in Part B indicate that enrichment of sediment with steroid estrogens occur downstream of Category C treatment plants. The levels of estrogens found in Danish sediments are comparable to or
lower than levels found in other European countries.
5.5 Background levels
The background or reference level of estrogenic activity in streams was, when studied in Part A, almost consistently under the limit of quantification (only 1 out of 11 barely above the LOQ).
The background level in lakes was somewhat higher, with a median level of 0.7 ng E2 equiv./L. In one of the reference lakes, Sorte Sø, the activity was about 6 ng/L and therefore this lake was
re-investigated in Part B. The analysis of the stored samples from 2004 confirmed the high activity found last year while a new sample taken in May 2005 only showed little activity.
A chemical analysis of a bank sample of lake water showed that half of the total estrogenic activity observed in 2004 could be explained by the presence of steroid estrogens. This indicates that a hitherto
unknown (and not immediately visible) anthropogenic contamination source may exist in the vicinity of the lake.
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Version 1.0 March 2006, © Danish Environmental Protection Agency
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