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Causes, Effects and Control
By R M Harrison
The Royal Society of ChemistryCopyright © 2014 The Royal Society of Chemistry
All rights reserved.
Chemical Pollution of the Aquatic Environment by Priority Pollutants and its Control
OLIVER A.H. JONES AND RACHEL L. GOMES,
It is difficult to imagine the modern 21th century lifestyle without the mobile phones, tablet PCs and social media that the majority of the general public have become accustomed to. Such technology is heavily reliant on chemicals and chemical technology. For example, solvents are widely used in electronics as solders and for cleansing, stripping, and degreasing operations and encapsulations. Solvents are also the cause of a significant portion of workplace hazards and exposure problems in not only the electronics industry but many others as well, for example agriculture, biotechnology and pharmaceuticals. The chemical industry is an important pillar of the modern world economy and the chemical industry affects nearly every part of our daily life.
Biological and physico-chemical processes operating in aquatic systems can remove pollutants from circulation, fix them more or less indefinitely, or degrade them to less harmful compounds. The self-purification capacity of many aquatic systems has led to their use for the indiscriminate disposal of society's waste in the past. While the pollutants themselves are often invisible to the naked eye, their impact on water resources and aquatic life is often quite conspicuous. Pollutant discharges may cause fish kill events, noxious smells or even change the colour of the water, all of which are easily perceptible to the casual observer. However, there are also many chemical pollutants that may cause harm to the health of a watercourse while not affecting its outward appearance. It can be both difficult and expensive to remediate water pollution, and the future use of the water may be affected by the presence of chemicals.
Awareness of the issues involved with the presence of chemicals in the environment has been high since Rachel Carson drew attention to the negative effects of the indiscriminate use of pesticides in the early 1960's. Since that time, a growing environmental movement and the wide-ranging impact of social and digital media means that the public is often bombarded with sensational headlines and stories about pollution by both the scientific and mainstream press: from the greenhouse gas emissions generated by shipping food around the globe through to heavy metals from waste electrical and electronic equipment, and, most recently, nanoparticles and the other emerging environmental contaminants such as disinfection by-products, pharmaceuticals and hydraulic fracturing or fracking substances (see section 1.5.4). In many such articles, terms such as "contamination" and "pollution" are often used somewhat interchangeably. It is important however, to make the distinction between them.
Contamination is simply the presence of a substance in a given sample where there is no evidence of harm. Pollution is contamination that results in, or can result in, adverse biological effects to individuals or communities. All pollutants are therefore contaminants but not all contaminants are pollutants. This means that differentiating pollution from contamination cannot be done on the basis of chemical analyses alone because such analyses provide no information on factors such as bioavailability or toxicity which influence whether a chemical presence actually causes harm. In addition, not all contaminants or pollutants are chemical in origin. Many different forms of pollution in the aquatic environment exist. These can be summarised as:
– Toxicity: acute or chronic toxicity causing severe damage (including death) to aquatic or human life.
– Sub-lethal toxicity: such as endocrine disruption, physical impairment, reduction of immunological/biochemical function or changes in biodiversity.
– Deoxygenation: lack of oxygen in the water reducing biodiversity.
– Spread of non-native and or invasive species to new systems.
– Eutrophication: excess nutrients giving rise to excessive growths of some organisms.
– Temperature: usually heat, for example from power station cooling systems.
– pH level changes; changes in H+ levels in a water body may affect both chemical and biological processes; e.g. acid rain linked to reduced shell formation ability in molluscs.
– Aesthetic: visual nuisance caused, e.g. litter, algal blooms, discoloration and smells.
– Noise: seismic surveying, shipping, boat traffic, pile driving and navy sonars are all sources of marine noise pollution that can affect the health of marine mammals.
– Light: increasing intentional and unintentional illumination of the coastal zone and near-shore (and increasing the deep sea) can interfere with the feeding, reproductive and migratory behaviour of some species.
It is important in pollution regulation to remember the "Source–Pathway–Receptor" model. Even the most potent toxin is harmless as long as it is isolated or contained and a compound designed to target a specific receptor is unlikely to have an effect in an organism that lacks such a receptor. It is also helpful to keep in mind one of the underlying principles of toxicology; namely that the dose makes the poison. All chemicals - even water and oxygen - can be toxic in certain amounts (although not all organisms respond the same way to chemicals at all stages of their life cycles). For example excessive heat will kill many species, either directly or by reducing the amount of O2 than can be dissolved in the water body concerned. Many serious pollution incidents are caused by spills of seemingly harmless substance such as milk or sugar. These substances are not directly toxic in themselves; in fact they have the opposite effect. Their high organic content increases bacterial growth, which causes a concomitant decrease in dissolved oxygen levels. In some cases the milk itself could also be contaminated, for instance by radiation following a radiological accident such as the Chernobyl disaster which contaminated fields and animals across Europe in the late 1980 s and the more recent Fukashima incident in Japan in March 2011; the impact and fallout of which was felt (albeit weakly) as far away as Western Europe. Such incidents are of course thankfully, very rare.
So, in the 21st century, society cannot function in the way in which it has become accustomed without producing pollution but left unchecked, such pollution will eventually undermine the functioning of said society. Consumers are currently encouraged to do their part, for example to reduce food miles by shopping locally, and to offset their carbon footprint by funding an equivalent carbon dioxide saving elsewhere (for example by investing in renewable energy projects). However, these are small savings. To ensure chemical pollution does not cause serious and irreparable damage to the environment there must be checks and balances in place to minimise the release of certain pollutants and the harm they could potentially cause. Such techniques may be economic and/or legal instruments. However, not everything can be regulated and it would not be economically or physically viable to do so. Thus, despite the fact that almost anything can be a pollutant, certain chemicals have been identified in regulations at a national, or increasingly international level, as being priority chemicals for control. Such pollutants generally meet one or more of the following criteria:
– They are frequently detected by environmental monitoring programs.
– They are toxic at low concentrations.
– They bioaccumulate.
– They are persistent.
– They are carcinogens.
For many of these substances the precautionary principle has been applied. Here the target is for no contamination to occur but there are different approaches and philosophies as to how to achieve the best environmental results.
1.2 POLLUTION CONTROL PHILOSOPHY
The public tend to think of pollution control in terms of mandatory regulations and there is no doubt that these are very important for environmental protection but they are only part of the solution. Other tools such as, environmental education, economic instruments, market forces and stricter enforcements all have roles to play in pollution control. Given the range of control measures available for environmental protection, preventing and controlling the release of priority chemicals to the aquatic environment can still be complex and challenging.
Controlling pollution to an environment has tended to rely on standards or objectives that are in some way measurable. The types of standards may be broadly divided into standards set by reference either to the target being protected, or the source of the pollution. The latter being further divided into standards covering emissions, process, product and use (see Table 1.1).
Standards may also be considered precise where there is a defined quantifiable minimum or maximum value for a particular or range of pollutants, or imprecise (classifying the health of a river or lake as fit to support fish for example), requiring the use of Best Available Techniques (BAT) or Best Practicable Environmental Option (BPEO). Together these provide an integrated framework where the use of one is not to the exclusion of another.
For environmental protection, the traditional command and control (CAC) practices are also complemented and supplemented by market-based economic instruments (EIs). EIs function through their impact on market signals, utilising prices or economic incentives/deterrents to achieve environmental objectives. There are five broad categories of EIs covering: charges, subsidies, deposit or refund schemes, the creation of a market in pollution credits, and enforcement incentives.
EIs offer the incentive and power for an industry or consumer to realign their rights and responsibilities and act in a more environmentally responsible manner. Some EIs are self-standing, whilst others work within the regulatory framework linking costs to the prevention, reduction or clean-up of pollution. For example, in England, the Environment Agency (EA) in carrying out any works, operations or investigations to prevent or remediate water pollution is entitled to recover expenses reasonably incurred from any responsible person under the Water Resources Act 1991 and 2009 Amendment.
These market-based EIs, along with other alternative control procedures, such as voluntary schemes and information systems, have been developed in response to growing awareness from governments of the need to increase the range of tools for controlling chemicals and encouraging environmentally responsible behaviour. Given the range of control measures available for environmental protection, preventing and controlling the release of priority chemicals to the aquatic environment can still be difficult.
Chemicals have the potential to gain entry to the aquatic environment at any stage in their life cycle (see Figure 1.1) and entry may be through a variety of avenues.
The routes through which priority chemicals may enter the aquatic environment can be broadly categorised into point and non-point (diffuse) sources. A point source release is from a discrete location, be that a pipe or some other single identifiable localised source, e.g. effluent from a sewage treatment plant or an oil spill. Non-point, or diffuse pollution, sources are emitted indirectly from multiple discharge points and tend to be intermittent, occurring less frequently or in less quantity to point sources, e.g. unconfined runoff from agricultural or urban areas into a water body.
Pollution control has traditionally focused on point sources due to the comparative ease in identifying and regulating a single pollution locale entering a water body. Strict requirements have been introduced to tackle the largest point sources on discharges to water and sewer, e.g. The Urban Waste Water Treatment (England and Wales) Regulations 1994 and the 2003 Amendment. This has encouraged industry to develop technologies able to reduce or remove chemical pollutants in the effluent to meet these regulations, which has led to substantial improvements in the quality of the receiving water body over the past years. However, sewage can still act as a conduit for pollutants to affect water quality due to sewer overflow, pipe failure, or where control measures have failed.
Similarly, the improvements in water quality brought about through the control measures imposed for point sources have also led to the realisation of, and additional focus on, the relative contribution of non-point sources to water pollution. Attention and control measures have therefore come to focus on and incorporate these non-point sources to facilitate further improvements in water quality. Environmental policy and practice in the last 20 years or so increasingly highlighted the need to develop a more holistic approach to environmental control and this has, and is influencing the philosophy of pollution control (see Table 2.1).
However, in some cases, the fines water companies face for polluting the environment are relatively small. For instance, although a sustained reduction in pollutant discharges from wastewater treatment works has been achieved in England and Wales through regulation over the past 20 years, in 2011 industrial sites caused 39% (240) of all serious pollution incidents. This is more than in 2010 (172 or 27%). This increase was due to more incidents from water company owned assets and waste management facilities. Indeed, in 2011, water company owned assets caused 120 serious pollution incidents in the UK (half of the incidents from sites regulated by the Environment Agency). This is almost double the number of incidents in 2010 (65 incidents) and the same as recorded by the EA in 2000. Of the 120 incidents, 101 were within the sewer or water network, and 19 were from permitted sites such as wastewater treatment works. Some of these spills were of quite toxic substances. For instance, virtually all releases of tributyltin (TBT) to water in 2011 came from water companies.
Environmental prosecutions in England and Wales in 2011 also make sober reading. In total 178 separate companies were fined for environmental offences in 2011, compared with 179 in 2010 and 317 in 2005. Total fines for the whole sector came to just over £3.8 million. This is lower than the total of £4.8 million in 2010 but this may be due to the large fines levied on the companies responsible for the 2005 Buncefield explosion. These costs are very much lower than the investment required for even minor treatment plant upgrades and thus whilst acknowledging the efforts of water companies to reduce environmental contamination, it seems highly unlikely that purely punitive legal instruments are able to prevent aquatic pollution in this way unless the law on environmental pollution in the UK is changed substantially.
It is also probable that removing all possible pollutants from wastewater is likely to be not only physically almost impossible and economically undesirable; it also may not be the best approach for the protection of the environment. Aside from the high energy usage and associated increases in CO2 and other greenhouse gas emissions, improved effluent quality also increases the amount of sludge produced, which requires environmentally sound disposal. Balancing desired improvements in the quality of effluent discharges, with the desire to reduce energy consumption and sludge production during treatment, poses a considerable challenge to the water industry. In 2007 Jones et al. went as far as to suggest that it may be time to address a paradigm of wastewater treatment, which has previously been unchallenged; namely that increasing effluent quality can only be environmentally beneficial. In fact, when subjected to life-cycle analysis, large-scale investment into increasingly energy intensive treatments is seen to be environmentally unsustainable. This is because the benefits of improved effluent quality are often outweighed by the negative effects on the wider environment when process construction and operation are looked at as a whole.
The question then becomes one of diminishing returns and how much extra water utilities, and their customers, are willing to pay to remove an extra nanogram of a compound from wastewater effluent, even if a health effect is unlikely. It is also of note that even removing all pollutants and contaminants from sewage effluent would have no effect on the contributions of these compounds to the environment from other sources, such as agriculture and landfill leachates. Thus, market-based EIs, along with other alternative control procedures such as voluntary schemes and information systems, have been developed in response to the growing awareness from governments of the need to increase the range of tools for controlling chemicals and encouraging environmentally responsible behaviour.
Excerpted from Pollution by R M Harrison. Copyright © 2014 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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