|
Survey of Estrogenic Activity in the Danish Aquatic Environment 2 Strategy and design of the study2.1 Overall strategy 2.1 Overall strategyDEPA's project description in the tender documents calls for a broad investigation of the estrogenic activity in the Danish aquatic (freshwater) environment with a good geographic coverage of the environmental situation and the potential pollution sources. This request has been the cornerstone in the development of the overall strategy and the operational design of the investigation programme of the study to be described in this chapter. 2.1.1 Selection of scenarios and locations
2.1.2 Sampling
2.1.3 Biological testing and chemical analysis
2.2 Selection of sampling sitesThe requested scenarios (Section 1.3) were divided into three main categories, each containing a number of sub-categories:
A more detailed description of each main category and its sub-categories is provided in section 2.2.1 - 2.2.3. It was a general requirement to all sampling sites that they should be reasonably accessible by car (to a close distance), that sampling should be possible without site modifications or non-standard equipment, and, preferably, that relevant data on the site and its characteristics were available.
*: Treatment processes: **: Septic tanks An overview map of the selected locations is shown in Figure 2.1. Detailed information regarding the sampling such as site names and location, the planned sampling programme etc. is included as Appendix 5 to this Report.
Figure 2.1 Location of sampling sites. WWTP sampling sites are always associated with sampling stations in the receiving stream upstream and downstream the point of discharge. 2.2.1 Wastewater treatment plantsThere are 1,240 registered wastewater treatment plants in Denmark (Miljøstyrelsen 2004), ranging from simple facilities serving only a few people to technically advanced plants with a current load of up to about 500,000 PE. An overview of the number of plants within the six simplified technical categories applied for the purpose of this project together with their share of the total volume of municipal wastewater in Denmark is shown on the following page. It should be mentioned here that WWTPs with tertiary treatment processes such as sand filters, lagoons, or UV- or ozone treatment on the effluents deliberately were not selected for the investigation programme. The reason for this was to keep the number of factors influencing the WWTP performance (effluent quality) sufficiently low to enable conclusions to be drawn. Explanation of WWTP categories: A. MBND/MBNDC: Plants with Mechanical, Biological (phosphorus removal), Nitrification and Denitrification (usually by activated sludge) treatment processes for removal of nitrogen, which on a significant number of plants are complemented by Chemical precipitation. This category includes all major WWTPs in Denmark. B. MBN/MBNC: WWTPs basically with same technology as above, however, without the denitrification step, and therefore without removal of nitrogen (only conversion of ammonia to nitrate). Mostly relatively small plants. C. MB/MBC: Small, simple plants usually located in rural areas. D. M/MC: Very small plants, often not much more than big septic tanks. Generally speaking, the technologically most advanced plants are also the largest and at the same time those with the biggest share of their wastewater influent originating from industrial enterprises. Of course exceptions occur, e.g. if a small community is substantially influenced by one major local enterprise. It should also be mentioned that with respect to reduction of traditional wastewater parameters (e.g. COD, nutrients and suspended matter), the performance of the WWTPs largely fall into the same four main categories of traditional WWTPs that are used for classification in this project (Cat. A-D) (Miljøstyrelsen 2004).
As appears from the table the plants in category A are completely dominant with regard to volume of wastewater treated. The 30 largest plants (all >100,000 PE) are currently treating almost 50% of the total volume of municipal wastewater in Denmark. However, the majority of these WWTPs are situated at or near the coast and their effluents are discharged directly into the marine environment. Hence, such plants are of limited interest in relation to this project and its objectives. It seems likely that the smaller, and often more simple, WWTPs are relatively influential on the water quality of streams, rivers and lakes. Their treatment efficiencies are lower (as assessed by common water quality parameters) and, in addition, they often discharge into rather small water bodies. Thus, they may have a considerable impact on the total flow and quality of the stream including the estrogenic activity. For these reasons the number of WWTPs within each category of this study is more even than it should be if the share of the total wastewater volume alone was the determining parameter. Some general requirements to the character and state of the WWTPs were put forward to the Danish counties and others in the process of identifying and selecting the specific installations for the study. These were:
Within each of the six mentioned categories of WWTPs, two sites were selected for more detailed examination:
2.2.2 Other potential sources of pollution (open land sources)In addition to the WWTPs a number of other sources may contribute to the total estrogenicity in the aquatic environment, particularly in the open land. These potential sources are, within each sub-category, believed to be relatively homogenous in terms of release and composition of estrogens and, hence, only relatively few locations have been selected to characterise their respective contributions to estrogenicity. All samples in this main category were, in addition to the biological testing, analysed chemically. Category G - effluents from isolated houses Isolated single houses (mostly farmhouses) in the open land outside towns and villages are not always connected to a sewer but may discharge their domestic wastewater via field drainage systems, normally following an initial settling of particulate matter in a septic tank or similar. Such a settling system does, however, not offer much in terms of improvement of the general effluent quality and therefore an impact of such effluents with regard to estrogens cannot be excluded and may even under specific circumstances be significant locally. It was a requirement to the sites in this category that the effluent should be possible to sample without having to modify the installation. This turned out to be a problem and, hence, it became necessary to introduce "surrogate" samples from other sites (WWTPs) where sampling of wastewater of a quality believed to resemble that of septic tank effluents was possible. Categories H and I - drains from manure and sludge amended fields, respectively Huge amounts of liquid and solid manure from pigs and cattle are each year applied to agricultural fields as organic fertilizers. Similar to humans, domestic animals produce estrogens that potentially exhibit the same type of effect on fish and other aquatic wildlife as the human estrogens. Likewise, a significant volume of sewage sludge (with sorbed estrogens) is amended to arable soils as a means of waste disposal that concomitantly provides nutrients and improvement of soil structure and organic carbon content. When applied onto agricultural soil, these waste products can be said to undergo a type of treatment process similar to sewage in WWTPs as the soil micro-organisms will degrade a significant fraction of the estrogens while another will be sorbed onto the soil matrix. Still, cracks and other macropores in the soil may enable some leaching of the substances to drainage depth and subsequent release to the aquatic environment. Category J - Stormwater runoff from separate collection systems A significant fraction (about 50%) of stormwater runoff from separate collection systems in towns and along roads is emitted directly into water bodies. This potential source is anticipated to be an insignificant one with regard to steroid estrogens, but it is known from other investigations that surface runoff can contain significant concentrations of heavy metals and various xenobiotics including some with known or suspected estrogenic activity (e.g. Arnbjerg-Nielsen et al. 2002; Kjølholt et al. 1997). Sampling for this category was done in the retention basins where an integrated figure of the quality from a whole rain episode could be obtained without having to install and operate flow-proportional equipment. Retention basins that were dry in between rain episodes were selected for the sampling. Category K - Fish farms Fish are very sensitive to estrogens in their environment but they also produce and excrete such substances themselves in low amounts. Therefore, a few trout fish farms are selected to investigate whether a large number and high density of fish in one place results in a measurable increase in estrogenic activity. Several types of fish farms exist, the most common being one producing sexually immature trouts for individual consumption. Other trout farms also rear mature fish for production of eggs or fry. Category K was investigated by testing/analysis of samples taken up- and downstream the effluent points. One farm of each of the mentioned main types was selected for the study. 2.2.3 The freshwater environmentThe environmental samples are sub-divided into a number of categories defined on basis of the anticipated level of exposure to estrogens from either urban or open land sources. Within each category a few sites were selected for more detailed examination i.e. they were sampled twice during the course of the study (the others only once), and the samples were not only tested biologically but also analysed chemically. Category L - streams/rivers receiving WWTP effluents For each of the selected WWTPs the stream/river receiving the treated effluent is also sampled upstream and downstream the point of discharge. Hereby it is attempted to identify and, if possible, semi-quantify the impact of WWTP effluents on surface water quality. The distance of the sampling point relative to the discharge point is determined by the width of the receiving stream/river as this is easy to use as a measure of when complete mixing of effluent and stream water has been achieved. Upstream samples are taken just 2-3 widths upstream while downstream samples are taken approximately 10 x river width from the discharge point. At the WWTPs selected for more detailed examination, some additional L-samples were taken 100 x river width downstream. Categories M and R - generally exposed/affected streams and lakes, respectively By "generally exposed/affected" is meant that no nearby point sources are evident but in the catchment of the stream/river (Cat. M) or the lake (Cat. R) both drained fields, single houses and towns with WWTPs are present, which may affect the general water quality. Most of the upstream samples from Category L can also serve as examples of "generally exposed" streams and rivers (Category M), as they are not located in reference areas. Some upstream L-samples are, however, taken in urban areas and are for the purpose of serving as "generally exposed" streams put in their own sub-category; LU(U). Categories N and O - Streams/rivers and lakes in husbandry areas, respectively Information from the Danish counties has been used to select a limited number of streams/rivers and lakes in areas with high densities of pigs and/or cattle to elucidate whether this type of agricultural activity and the associated need for waste disposal on the fields is reflected in a concomitant higher level of estrogenic activity than in general. Categories P and Q - reference streams and lakes, respectively It is also important to know whether estrogenic activity is an inherent property of aquatic environments in the sense that such activity can be detected even in places without known inputs from anthropogenic sources including husbandry. Therefore a number of small streams and lakes in catchments known or assessed to be practically without human settlements and/or activity have been identified for the study. 2.2.4 Special investigationsThe special investigations mentioned in the overview table in the introduction to Section 2.2 consisted of a study on three selected WWTPs representing different treatment technologies with the aim to determine the variation in effluent composition during 24 hours (and the error introduced by spot sampling compared to flow-proportional sampling). The investigation is described thoroughly in Section 4.1.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
