J. W. Birkett
2.1 INTRODUCTION
2.1.1 Point Sources ... 36 2.1.2 Nonpoint Sources ... 36 2.1.3 Hydrological Control ... 37 2.1.4 Groundwater Pollution ... 37 2.1.5 Other Sources ... 38 2.2 Specific Sources Relating to Endocrine Disrupting Chemicals (EDCs) ... 38 2.2.1 Steroids ... 38 2.2.2 Phytoestrogens ... 41 2.2.3 Organo Oxygen Compounds ... 42 2.2.3.1 Bisphenol A ... 42 2.2.3.2 Phthalates ... 43 2.2.3.3 Dioxins ... 43 2.2.4 Organotin Compounds ... 44 2.2.5 Surfactants ... 45 2.2.6 Polyaromatic Compounds ... 47 2.2.6.1 Polyaromatic Hydrocarbons (PAHs) ... 47 2.2.6.2 Polychlorinated Biphenyls (PCBs) ... 48 2.2.6.3 Brominated Flame Retardants ... 49 2.2.7 Pesticides ... 51 References ... 52
2.1 INTRODUCTION
Endocrine disrupting chemicals (EDCs), as well as other pollutants, have a variety of sources. These sources may have implications for human exposure, effects in wildlife, and effects or accumulation within the environment. Moreover, many EDCs have been found to be ubiquitous in the environment. Generally, sources of pollution fall into two main categories:
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36 Endocrine Disrupters in Wastewater and Sludge Treatment Processes
1. Point sources
2. Nonpoint sources (or diffuse sources)
Table 2.1 summarizes point and nonpoint sources 2.1.1 POINT SOURCES
A point source is a definitive point of entry of a pollutant into an environmental medium (generally a watercourse). It could be an effluent discharge pipe, a storm- water overflow, or a known point where waste is repeatedly dumped. Point sources tend to be easier to control than nonpoint sources, so, as far as possible, nonpoint sources are converted to point sources.
Point sources vary according to the specific catchment area under study. In a river system, sewage treatment works tend to constitute the main sources of pollution.
This fact illustrates the success of the authorities and regulatory bodies in minimizing other sources.
2.1.2 NONPOINT SOURCES
Nonpoint sources (sometimes called diffuse sources) do not have a definitive point of entry. Good examples of nonpoint sources are atmospheric deposition and runoff.
The actual point where the pollutants enter depends on the type of source, its location, and on the physical form of the pollutants. If the pollutants are gases or fine airborne particles, they can fall to the ground directly with rain. The rain can also wash particles that have been deposited on surfaces into nearby watercourses. If the pollutants are soluble, they can be transported long distances in the water. During storms, large particles, including soil, can be washed down from the land into water bodies. These may have pollutants such as pesticides attached to them.
TABLE 2.1
Point and Nonpoint Sources
Point Sources Nonpoint Sources
Discharges from sewage treatment works to rivers
Runoff and underdrainage from agricultural land into rivers
Discharges of industrial wastewaters to rivers General contamination of recharge rainfall to outcropping aquifers
Discharges of farm effluents to rivers Septic tank soakaways into permeable strata Discharges from small domestic sewage
treatment plants to rivers
Washoff of litter, dust, and dry fallout from urban roads to rivers
Discharges by means of wells or boreholes into underground strata
General entry of sporadic and widespread losses of contaminants to rivers
Discharges of collected landfill leachate to rivers Seepage of landfill leachate to underground strata and rivers
From Lester, J.N. and Birkett, J.W., Microbiology and Chemistry for Environmental Scientists and Engineers, 2nd ed. E & F.N. Spon, London, 1999. With permission.
Sources of Endocrine Disrupters 37
Nonpoint source pollution transport processes in urban areas are likely to be different than those in rural areas. There are several reasons for this:1
1. Quite a large part of urban areas are covered by impermeable materials.
Thus, quite a lot of the rainwater runs off and eventually enters drains and sewers.
2. In urban areas, less soil is exposed so less erosion, and hence transport of soil particles into surface waters, can be expected.
3. In urban areas, pollutant loadings are mainly affected by the accumulation of litter, fallout, and road traffic. In rural areas, most of the pollution is due to the erosion of soils.
4. In the long term, almost all of the pollutants deposited on impermeable surfaces in urban areas (except those removed by external processes such as street cleaning) will eventually end up as surface runoff. In rural areas, deposits can be incorporated into the soil where their removal rate is reduced.
2.1.3 HYDROLOGICAL CONTROL
This refers to man’s interference in the movement of water through natural channels.
The result is a nonpoint source pollution that can directly or indirectly affect water quality. Examples are the construction of drainage and irrigation systems, dredging in order to create or maintain navigable stretches of water, and the construction of dams and reservoirs.
Dredging can cause water pollution because pollutants that were previously held tightly within the sediment can be redissolved or resuspended in the water during the dredging operation. Dredging spoil is often dumped back into the water at a point remote from where it was taken. This can have the effect of transporting any pollution from one place to another.
2.1.4 GROUNDWATERPOLLUTION
Most human activities at the land’s surface cause some change in the quality of water in the aquifer beneath them. The importance of the effect of a particular activity is related to the amounts and types of contaminants released. The severity of an occurrence is also related to the ability of the soil and groundwater system to degrade or dilute the contaminants, and the degree to which the contamination will interfere with uses of the water. Contamination is usually more serious in a drinking water supply than in water for other uses.
Groundwater is a good source of drinking water because of the properties of the soils that purify rainwater as it percolates through to the aquifer. This particularly applies to suspended matter, which is effectively filtered out by the strata overlying the aquifer. Except where contaminated water is injected directly into an aquifer, essentially all groundwater pollutants enter the aquifer through recharge water from the land surface.
38 Endocrine Disrupters in Wastewater and Sludge Treatment Processes
The main sources of groundwater pollution arise from industrial, domestic, and agricultural sources. Industrial sources are industrial effluents, accidents (e.g., leakage from pipes and tanks), and rainwater that infiltrates and percolates through solid waste deposits. Solid wastes are deposited in landfill sites. Landfills that take hazardous waste are often sited in areas where there are impermeable strata, such as clay, or where clay linings have been deliberately installed to prevent leachate from escaping.
Domestic sources of groundwater pollution fall into more or less the same categories as the industrial sources. Leakage from septic tanks and percolation of rainwater through landfills containing domestic refuse are the main risks.
Agricultural sources are potentially the most dangerous because they are nonpoint sources, and percolation through soils into the groundwater can occur over wide areas.
As a result, fertilizers, minerals, herbicides, and pesticides can all enter aquifers.
There is also a potential risk from the disposal of sewage sludge on agricultural land, which, in addition to the sea, is another major disposal outlet for this material.
Endocrine disruption manifesting as reproductive and behavioral abnormalities observed in fish has been primarily attributed to EDCs in sewage effluent discharged into watercourses. In addition to the types of discharges already mentioned, con- tamination of the aquatic environment can be caused by numerous other sources.
These sources of EDCs are summarized in Table 2.2.
2.1.5 OTHER SOURCES
For the human population, the most important source of EDCs by far is food. Some of these compounds are utilized in food production and packaging, which has prompted concern that diet may be an exposure route for EDCs.20 Examples of this include pesticide residues on fruit and vegetables, use of plastic wrapping, and the leaching of compounds from can linings.21 These, together with other sources for EDCs, are highlighted in the following section.
2.2 SPECIFIC SOURCES RELATING TO ENDOCRINE