CHAPTER 1
Chemical Pollution of the Aquatic Environment by Priority Pollutants and its Control
B. CRATHORNE, Y. J. REES AND S. FRANCE
1.1 INTRODUCTION
It is difficult to imagine a modern society without the benefits of chemicals and the chemical industry. Pharmaceuticals, petrochemicals, agrochemicals, industrial and consumer chemicals all contribute to our modern lifestyles. However, with the rise of chemical manufacture and use has come increasing public awareness and concern regarding the presence of chemicals in the environment.
There is an important distinction between the presence of chemicals in the environment (contamination) and pollution. Although these terms tend to be used in similar ways in everyday speech and journalism, in scientific areas there is a broad consensus that the term 'contamination' should be used where a chemical is present in a given sample with no evidence of harm and 'pollution' used in cases where the presence of the chemical is causing harm. Pollutants therefore are chemicals causing environmental harm.
The effects of water pollution can be summarized as:
• aesthetic: visual nuisance caused, e.g. litter, discoloration and smells
• temperature: usually heat
• deoxygenation: lack of oxygen in the water
• toxicity: acute or chronic toxicity causing damage to aquatic or human life
• sublethal toxicity: such as endocrine disruption or changes in biodiversity
• acidity/alkalinity: disturbance of the pH regime
• eutrophication: nutrients giving rise to excessive growths of some organisms
Any chemical can become a pollutant in water causing one or more of these effects if it is present at a high enough concentration. For example, serious pollution incidents result from spills of sugar and milk, substances which contain a high organic content. In fact, the majority of pollution incidents in the UK continue to be due to gross organic pollution. In 1998 sewage accounted for 24% of the l7 863 substantiated pollution incidents in England and Wales with oil being the single most frequent cause, accounting for 30%. Such organic pollution is caused by effluents containing biodegradable organic chemicals which generally act as pollutants, not because they contain chemicals at concentrations that are toxic, but rather the reverse. They contain chemicals that provide food for microorganisms which multiply rapidly as a result of the increased food input. The microorganisms, in the process of growing and oxidizing the organic chemical foodstuff, use up the dissolved oxygen rapidly which in some cases leads to the death of higher organisms, like fish.
Despite the fact that any chemical can be a pollutant, certain chemicals have been identified in regulation or by international agreement as being 'priority chemicals for control'. Such chemicals have generally been selected based on the following criteria:
• the chemicals are frequently found by monitoring programmes
• they are toxic at low concentrations
• they bioaccumulate
• they are persistent
• they are carcinogens
While a few years ago it would have been possible to quote the List I substances in the Dangerous Substances Directive (see Section 1.3.1) as being the priority pollutants, it is no longer possible to identify a single list. Different chemicals are priority pollutants in different contexts.
For many of these priority pollutants, the elimination of pollution is not considered sufficient by many and, applying the precautionary principle, targets of 'no contamination' have been set. This is demonstrated by a recent agreement between the North Sea countries, through the Oslo and Paris Commission, to reduce discharges, emissions and losses of specific hazardous substances continuously, with the ultimate aim of reducing concentrations in the marine environment to near background values for naturally occurring substances and close to zero for man-made synthetic substances.
1.2 POLLUTION CONTROL PHILOSOPHY
Preventing pollution of the environment by priority chemicals is very complex as chemicals are released and can gain entry to the environment at any stage in their life cycle (Figure 1.1), from development and testing, through manufacture, storage and distribution through to use and finally disposal.
Releases to the environment can broadly be categorized into point source releases, i.e. specific inputs from an industrial site or sewage works, etc., and diffuse or non-point source releases. Controls have tended in the past to concentrate on tackling the largest point sources and introducing strict requirements on discharges to water and sewer. A great deal has been achieved but, whilst the source and single media based controls have been effective, we are left with other problems. In the last decade or so the emphasis on priority pollutant control has shifted away from control of point sources towards control of diffuse sources. The main reason for this is the success achieved by control of point source pollution. A combination of factors has caused this, principally:
• new technology enabling priority pollutant use to be avoided, e.g. new pesticide discovery and new production processes
• improved pollution control technology
Given the success in this area, the relative contribution of diffuse sources has risen and attention has come to focus on these areas to facilitate further improvements. By their nature, diffuse sources require different types of regulatory control from those for point sources.
Experiences over the last few decades have also highlighted a need to look more holistically at environmental controls and specifically to:
• take a more integrated view of the environment.
• consider the impacts of mixtures on the environment.
• look beyond national borders.
• move away from an end-of-pipe approach.
• introduce a wider range of control measures.
Taking a more integrated view. It is widely recognized that control of pollution is not a single environmental media or single industry issue, and integrated pollution control and cross industry reviews are now routine. The implementation of Integrated Pollution Control (IPC) has played an important role in introducing a more holistic control philosophy to environmental management. IPC applies to releases from the 'most polluting industrial processes'. The system tightened pollution control requirements by introducing the concepts of Best Available Techniques Not Entailing Excessive Costs (BATNEEC). Releases of the most polluting substances must be prevented or, where this is not possible, minimised and rendered harmless. For processes resulting in releases to more than one environmental medium the Best Practicable Environ- mental Option (BPEO) has to be identified in order to minimize the impact of the process on the environment as a whole. This approach will be further advanced under the IPPC Regulations which apply to a wider range of processes and require a more wide ranging criteria in the consideration of best available techniques (see Section 1.3.3).
A good example of the complex interactions that can occur, at least in theory, is the report of the potential accumulation of HCFC breakdown products in seasonal wetland areas. The HCFCs (hydrochlorofluorohydrocarbons) are expected to break down in the atmosphere fairly rapidly. This is the reason they are preferred over the CFCs (chlorofluorohydrocarbons). However, trifluoroacetic acid, which some HCFCs are expected to produce, is very stable and will wash out from the atmosphere in rain. In areas like seasonal wetlands which have high evapotranspiration rates the trifluoroacetic acid may concentrate to levels which may damage plants. At present, this is based on theory and modelling but it does illustrate the complexity of environmental processes.
Considering the impacts of mixtures. An issue currently being considered is how best to deal with mixtures of chemicals. Chemicals that enter the environment usually do so as wastes or by-products, and as such are mixed with other chemicals. They may interact when they are mixed in an additive, synergistic or antagonistic way. They may produce breakdown products, by-products or react to form new substances in the waste stream or in the environment. Whilst controls on individual chemicals can be effective, they cannot take account of these real environmental situations.
Direct Toxicity Assessment (the use of ecotoxicity tests to assess complex chemical samples) is being considered as a control tool for chemical mixtures for both process and emissions control. In addition, in order to provide a more integrated view of the state of the environment, ecological monitoring is essential. Given that the ultimate aim of chemical control is protection of the environment it is only by measuring improvements in ecological quality that the ultimate effectiveness of chemical control measures and other control measures can be determined. This focus on ecological quality is the basis for the new approach to water management in the recently adopted Water Framework Directive (see Section 1.3.4).
Looking beyond national borders. Recognition that pollution does not recognize national borders, particularly for priority pollutants which tend to persist in the environment for long periods and can therefore be transported long distances, has led to growing international action on priority pollutant control. There are many initiatives to protect the aquatic environment from priority pollutants particularly for the protection of marine waters (see Section 1.3).
Moving away from end-of-pipe controls. Government, regulatory agencies and industrial initiatives have recognized a hierarchy of approaches to priority pollutant control:
• replace: use another, more environmentally friendly chemical
• reduce: use as little of the priority pollutants as possible
• manage: use in a carefully managed way to minimize accidental or adventitious loss and waste
This is reflected in the requirements under IPC which require that emissions of the most harmful substances are 'prevented or if that is not possible minimized and rendered harmless'.
Introducing a wider range of control measures. Traditionally the instruments for controlling chemicals have been regulations setting limits for discharges to water or banning a chemical from specific or all uses (see Sections 1.3 and 1.4). However, regulation has been recognized as being a rather blunt instrument with which to achieve continuous improvement, particularly for diffuse sources. Specifically in relation to priority pollutant control it has been difficult to find ways of encouraging replacements of priority chemicals by other, more benign substitutes. It has also been recognized that if the regulation can work with the 'grain' of the market, i.e. the normal market forces – supply and demand, consumer choice etc. – it will be more effective. Governments are aware of a need to increase the tools for controlling chemicals by introducing voluntary schemes, information systems and economic incentives to encourage more environmentally friendly practices (see Section 1.5).
The important points to emphasize here are that the regulation and control of priority pollutants:
• is not just a case of tightening up on discharge consents as diffuse sources can be important and can dominate in some cases
• is an international issue
• requires a portfolio of complementary activities based on a hierarchy of replace–reduce–manage
1.3 REGULATION OF DIRECT DISCHARGES
In the UK, all direct discharges to water and indirect industrial discharges to sewer are controlled via permitting systems. The legislation establishing these systems is described in more detail in Chapter 20, but briefly the main Acts are:
• The Environmental Protection Act 1990 – for discharges from the most polluting industrial processes.
• The Water Resources Act 1991 – for all discharges direct to controlled waters except those covered under IPC.
• The Water Industry Act 1991 – for discharges to sewer.
The priority pollutants controlled under these permitting systems and the standards which apply are heavily influenced by international initiatives, in particular several key EU Directives and agreements made at the North Sea Conferences and by the Oslo and Paris Commission (OSPAR).
The permitting systems adopt the two general approaches for controlling direct discharges to water; the use of Environmental Quality Objectives/ Environmental Quality Standards (EQO/EQS) and Uniform Emission Standards (UES). This difference lies at the heart of a long running debate in Europe with the UK favouring the EQO/EQS approach and most other countries favouring UESs.
The EQO/EQS approach seeks to define the use that is to be made of a given water body, examples would be 'use for drinking water abstraction' or 'use for the support of salmonid fish populations', which defines an Environmental Quality Objective (EQO). In order to secure the objective in the presence of dangerous chemicals, Environmental Quality Standards (EQS) are needed. These are concentrations of the chemicals concerned below which there is expected to be no impact on the EQO. Emission limits for effluents can then be established by taking account of dilution capacity within the receiving waters on the basis that the EQS limits must not be exceeded outside the immediate impact zone (also called the mixing zone).
The UES, or limit value, approach sets limits for the concentration of dangerous substance in the effluent, without taking specific account of the available dilution capacity or the presence of other inputs to the same water body. The UES limits are usually expressed as effluent concentrations (monthly flow-weighted averages) with additional limits on daily values – the daily values being usually a factor of two to four higher. Values are also expressed as a total amount of substances per unit of production or use, e.g. 40 g CCl4 per tonne of production.
At a technical level there has been a growing recognition that the most sensible approach to pollution control is a fusion of the two approaches as adopted in the Integrated Pollution Control system (see Section 1.3.3).
1.3.1 Dangerous Substances Directive
The Dangerous Substances Directive (76/464/EEC) was adopted in 1976 to provide a framework for eliminating or reducing pollution of inland waters by particularly dangerous substances. In this Directive chemicals are either placed on List I, which has come to be known as the 'Black' List, or on List II, the 'Grey' List. Different control procedures are applied to chemicals on these lists. Those on List I have limit values and EQSs agreed at Community level. These appear in daughter Directives, e.g. Directive of 26 September 1993 on limit values and quality objectives for cadmium discharges (93/513/EEC). (Confusingly, in Directives the Commission uses 'quality objective' to mean the same as EQS in the discussion above!) The List I chemical categories are given in Table 1.1 and specific chemicals agreed for control as List I chemicals are provided in Table 1.2. In 1982 the Commission also published a list of l29 potential List I chemicals selected by the Commission on the basis of production volume and estimates of toxicity, persistence and bioaccumulation.
List II chemicals are to be controlled by using the EQO approach using quality standards set nationally. Member States are also required by the Directive to establish programmes to reduce pollution by these substances. The families of chemicals identified as List II are given in Table 1.3 and those for which National Quality Standards have been set are given in Table 1.4.
