Rationale for level of impacts of down the drain chemicals on habitats
Figure 4.3 indicates the key routes of environmental exposure to down the drain chemicals. By far the highest volumes of discharges result from end consumer use. In Europe most consumer emissions are into municipal sewerage systems which can lead to discharges of treated or untreated effluent into receiving waters or to soil as contaminants in aqueous sewage (as irrigation water) or sewage sludge (applied as fertiliser). Therefore, habitats likely to experience highest exposures are those closest to the points of discharge, i.e. lotic freshwaters and transitional waters and cropland / grassland. Coastal waters can also be the primary receiving environment but, in general, may provide greater initial dilution of effluents than freshwater systems. Lentic systems are often by-passed to avoid discharging into slowly moving water but may be exposed via inflowing lotic water. As the distance from the point of discharge increases towards the open ocean, exposure is expected to rapidly reduce because of loss processes (biotic and abiotic degradation and partitioning to solids) and further dilution. Terrestrial habitats other than cropland / grassland are unlikely to receive direct applications of aqueous sewage and sludge, and so will only be exposed via indirect routes such as transport in ground water or irrigation water.
Figure 4.3: Emission routes of chemicals in consumer products and pharmaceuticals into the environment
The chemicals present in consumer products and pharmaceuticals represent a wide range of chemistry in terms of physico-chemical properties and mode of toxic action. A proportion of the thousands of chemicals included in these categories are considered to have a non-specific mode of action and therefore, have potential to impact a wide range of SPUs. Others may be specific physiological targets and/or have higher potency for specific taxonomic groups, e.g. antimicrobial compounds, synthetic oestrogens, etc. However, for many chemicals the breadth of potentially affected species means that the lists of potentially impacted SPU will tend to be a comprehensive listing for each ecosystem service that they deliver.
Table 4.3: Potential impact of down the drain chemicals on specific ecosystem services (green: no impact; yellow: moderate impact; red: severe impact) and potentially impacted service-providing units (SPU)