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This research paper will brieﬂy deﬁne the term marine pollution and then go on to consider the historic growth of problems in this area and the perception of those problems. The main areas of concern in terms of marine pollution are then outlined and the international methods of regulating marine pollution problems are considered.
The term pollution is used widely and rather loosely. In the context of the oceans the UN sponsored Joint Group of Experts on the Scientiﬁc Aspects of Marine Pollution (GESAMP) oﬀered the following deﬁnitions (GESAMP 1982):
Contamination is the presence of elevated concentrations of substances in water sediments and organisms. Pollution is the introduction by man, directly or indirectly, of substances or energy into the marine environment (including estuaries) resulting in deleterious eﬀects such as harm to living resources, hazards to human health, hindrance of marine activities, including ﬁshing, impairing quality for use of seawater and reduction of marine amenities.
These deﬁnitions are extremely valuable because they draw an important distinction between human-induced changes in the concentrations of a substance somewhere in the marine environment (contamination) and actual damage resulting from this introduction (pollution). The oceans in total are vast and have a huge capacity to dilute, and in some cases break down, a discharge if time and physical processes allow this dilution and degradation capacity to be utilized. Acknowledgment of this capacity should not imply complacency about problems arising from human impacts on the ocean, but rather help focus concern on the most important issues.
2. Historical Developments
Major public health problems in developing cities in the Middle Ages led to the construction of primitive sewers to discharge wastes to local estuaries. Such discharge of wastes improved public health but caused pollution in estuaries such as the Thames in London from the fourteenth century onwards, promoting the earliest development of sewage treatment systems. However, until the twentieth century technological development was such that only the immediate coastal environment was signiﬁcantly contaminated by human activity. Despite this, the tragedy of the decimation of the great marine mammals by hunting demonstrates major and global human impacts on the marine environment from the eighteenth century onwards.
Concern over marine pollution grew from the 1950s onwards as it became clear that the ability of the marine environment to absorb discharges was not inﬁnite and that real damage was being done by human activity. Incidents such as the mercury poisoning at Minamata in Japan, the global contamination of the oceans by radioactive debris from bomb testing and by persistent pesticides such as DDT, and the eﬀects of the ﬁrst large-scale oil spills from sinking of the new giant oil tankers changed for ever the public perception of the vulnerability of the oceans to damage from human activity.
Investigations into these incidents also began to reveal the complexity of marine contamination and pollution issues. The saga of DDT illustrates that some contaminants can very eﬀectively become globally dispersed and furthermore can be concentrated up the food chain to cause major ecological damage far from source to nontarget organisms.
By contrast, while the eﬀects of an oil spill are locally catastrophic in the short term, the bacteria in the marine environment have the capacity to degrade such hydrocarbon material and hence the problem is relatively localized and short term. It is also now known that the biggest sources of hydrocarbons to the marine environment are not the rare catastrophic oil spills, but rather the chronic low-level operational discharges of oil, although the impacts of the two diﬀerent sorts of discharge are very diﬀerent. These examples illustrate that contaminants of the marine environment can be broadly classiﬁed into several groups.
Nondegradable. Elements such as lead and cadmium cannot be degraded, although they may become stored in sediments and largely removed from biological interactions.
Slowly degraded. Some organic compounds such as DDT and PCBs are only very slowly degraded over timescales of decades or longer. Radioactive material introduced to the marine environment decays over timescales controlled by radioactive half-lives which range from seconds to millions of years. In the case of both persistent organic and radioactive contaminants, intermediate decay products can also be toxic. As with nondegradable material, these compounds may be buried in sediments and eﬀectively taken out of the system long before they are fully degraded.
Readily degraded. The marine environment is a natural biological system containing a wealth of micro-organisms able to break down many organic compounds including substances such as sewage and oil. As noted later, however, the breakdown process itself and the products of that breakdown can cause serious environmental problems.
Since the 1950s there has been enormous growth in the scientiﬁc understanding of how the oceans function as a physical, chemical, and biological system. This has allowed a much better assessment of the local and global scale of marine contamination and pollution problems. However, it was still not until the early 1970s that the natural distributions of some important contaminants, such as cadmium, in the oceans were described. A basic understanding of the natural distribution of an element is clearly a vital prerequisite to assessing the likely contamination of the oceans from human impacts. In the case of entirely manmade substances such as DDT or artiﬁcial radionuclides, the situation is rather diﬀerent since their detection in the environment at any level implies contamination, although not necessarily pollution.
In recognition of the growing impact of human activity on the oceans, discharge controls on degradable and nondegradable materials have been introduced in many countries. These aim to minimize harmful impacts, based on the best available scientiﬁc understanding of likely eﬀects. There is clear evidence that these controls have had beneﬁcial eﬀects in many areas. The resulting declines in levels of lead and some radionuclides in the oceans, for instance, have been documented. However, the pollution arising from the use of tributyl tin (TBT) as an antifouling agent in the 1980s provides a warning that our control procedures are still far from being entirely eﬀective. Every year hundreds of new organic compounds are synthesized and used in industries around the world. The eﬀects of the inevitable resultant discharge are rarely known with certainty and there is growing concern over their possible eﬀects. The issue of possible estrogenic eﬀects of chemicals discharged to the environment represents an example of a new and disturbing pollution problem that we are a long way from understanding.
3. Current Concerns
A series of reviews of the marine environment have discussed the changing nature of pollution threats to the oceans and also suggested a broad consensus on the nature of current threats to the oceans (McIntyre 1995, Goldberg 1995, Huber 1999). The major issues of current and likely future concern center on the eﬀects of sewage and nutrient discharge, and the release of organic compounds including pesticides. The issue of marine litter is also still of concern, with evidence of damage to bird and marine life from the indiscriminate discharge particularly of plastic wastes from ships and the loss of drift nets. Regulations to reduce these problems exist, but policing such regulations on the high seas is almost impossible.
The global population is growing and the proportion of that population living near the sea is also growing. The waste discharges from that population will inevitably enter the marine environment, although this will hopefully be after basic treatment. Furthermore, the agricultural and industrial activity to sustain that population will inevitably result in discharges to the marine environment, even if these are minimized by the use of the best available technology. Thus it is the insidious eﬀects of this population growth that may pose the biggest threat to the oceans.
Sewage wastes contain many harmful micro-organisms. The public health eﬀects of coming into contact with these organisms either directly, via bathing, or in foodstuﬀs such as shellﬁsh, where they can become concentrated, is increasingly being recognized. Sewage wastes are rather quickly broken down by natural micro-organisms in the marine environment to release nutrients such as nitrogen and phosphorus. However, the breakdown of organic wastes such as sewage requires oxygen, or some other oxidizing agent. If the rate of breakdown of waste and associated oxygen consumption exceeds the rate at which oxygen is supplied, oxygen concentrations in the water will fall, leading, in the extreme case, to oxygen depletion and the loss of almost all animals as well as the production of noxious odors. This happened in the Thames estuary as London’s population grew and overwhelmed primitive waste treatment facilities. Improvements in waste treatment since the 1950s have restored the health of the Thames. Similar stories of damage from waste discharge and subsequent recovery with improved waste treatment can be told for industrialized estuaries around the world. They illustrate that we have the technology to mitigate the eﬀects of sewage discharges and to reverse the damage done.
Human perturbations have approximately doubled the ﬂuxes of the nutrients nitrogen and phosphorus through the environment, while the perturbation for the nutrient silicon is much less. Thus ﬂuxes and the relative proportions of the nutrients have changed as a result of human activity. Nitrogen and phosphorus ﬂuxes are projected to continue to increase in the future. The resulting inputs to the oceans have already led to eutrophication problems in some areas, although on a global scale human impact has done little to increase the vast natural nutrient inventory of the deep ocean. Problems are therefore focused on the coastal environment. Eutrophication describes the process of increased nutrient load stimulating the growth of phytoplankton, the microscopic algae that form the base of the food chain. A modest stimulation of phytoplankton growth has the potential to increase the phytoplankton stock and thereby provide more food for animals further up the food chain. However, excessive nutrient inputs coupled to inadequate dilution can lead to excessive algal growth which can settle into deeper water after death and consume all the available oxygen leading to the death of animals living in deep waters. The extent of such deep-water oxygen depletion depends critically on the physical water exchange processes which promote oxygen supply to the deep waters. Thus in areas of restricted mixing, such as the Baltic or Adriatic Sea, there are serious problems, while in the much more open North Sea the problem is less signiﬁcant, although all these areas receive major discharges of nutrients via rivers and the atmosphere.
Large-scale algal growth, or blooms, can also involve undesirable or toxic species and have a range of highly undesirable eﬀects. There is some evidence that such blooms may be increasing worldwide, although systematic studies to conﬁrm this are not available. Indeed, on an oceanic scale, or even a regional scale, it is often diﬃcult to quantify the level of human perturbation of the marine system, particularly since coastal and near-surface environments are characterized by great natural variability. Systematic studies of the marine environment are relatively recent, so we often do not have suﬃcient a time series of data to identify with conﬁdence concentration trends for many contaminants.
Pesticide use has many beneﬁts to human society, particularly in terms of increased food production. However, the release of chemicals into the environment which are designed to produce harmful biological eﬀects is inevitably a cause for concern. The use of some pesticides such as DDT and TBT are now severely restricted, although the extent and eﬀectiveness of such regulation varies widely from country to country. In developing countries the use of other pesticides is continuing to increase. These will inevitably escape into the wider environment and the eﬀect of low levels of these compounds individually or in mixtures is very poorly understood. The input of other potentially harmful organic compounds is also of continuing concern, as noted earlier.
3.4 Global Issues
In addition to these concerns over the direct contamination of the oceans, recently attention has turned to the role of the oceans within the larger global climate-regulating system. Heat and CO exchange between the ocean and the atmosphere are key elements in this system. The emission of gases, such as dimethyl sulﬁde (DMS), from the ocean also plays a major role in climate regulation. The response of these exchange processes to climate change represents a series of poorly understood feedbacks in the global climate system. This makes predicting the eﬀects of increasing concentrations of CO and other greenhouse gases particularly diﬃcult. Thus it is important to recognize that the oceans play a key role in the control of the whole planetary system, and hence that atmospheric pollution is linked to marine pollution.
3.5 Loss Of Marine Habitats
Marine pollution is usually considered in terms of inputs of chemical wastes to the marine environment. However, there are two major issues that represent simpler and more direct threats to the marine environment. First, there is clear evidence that almost all ﬁsheries worldwide are fully or overexploited. In the North Sea, for example, the clearest trend of environmental change is not of chemical contamination, but the vast decline in ﬁsh stocks. Globally half of the individual ﬁsh stocks are fully exploited and another 22 percent are overexploited.
The second issue is the physical degradation of coastal environments. In some cases this takes the form of total loss of habitat to reclamation. For instance, in the Humber estuary, the largest English estuary draining to the North Sea, more than 90 percent of the intertidal area has been lost to reclamation over the last 300 years. Similar losses have occurred in many other estuaries. In tropical areas half the mangrove forests have been lost to developments of some sort. These represent a massive loss of ecologically important wetlands and also loss of nutrient-processing potential. In other cases the habitat loss is not complete but involves a major reduction of ecological value. This problem is illustrated by the loss of many inshore coral reef systems to sedimentation. This occurs as changing land use patterns increase erosion and hence turbidity in the coastal waters, blocking light to the coral community and ultimately killing the corals. Eutrophication can have similar eﬀects. Intertidal areas and coral reefs also represent important components of coastal defense against erosion and ﬂooding. The destruction of these areas therefore represents economic as well as ecological losses.
4. Research And Regulation
Long-range transport is a feature of marine pollution issues, and hence national regulation alone is inadequate to protect the marine environment. There have been a series of initiatives focused on regional seas such as the Baltic, the North Sea, and the Mediterranean to achieve coordinated international action to manage the area. The United Nations Convention on the Law of the Sea entered into force in 1994, providing an international framework for the exploitation of the marine environment and also a requirement on states to ‘use the best practical means at their disposal’ to prevent and control marine pollution. While imperfect, these initiatives represent a growing realization that the oceans need to be managed at an international level to ensure their continued value for future generations.
There has also been a growing recognition that progress in managing the marine environment requires interdisciplinary scientiﬁc study involving chemists, biologists, physicists, and geologists. An important recent development has been the integration of social scientists in this work to describe the human pressures on the marine system and to consider future management options for the marine environment. An example is the recent valuation of the whole marine ecosystem at $20 billion dollars, although the methodology used is controversial. Most of the value assigned to the marine environment in this analysis is associated with the cycling and storage of nitrogen and phosphorus, and hence intimately linked to nutrient and sewage pollution issues. Huber (1999) noted ‘Environmental degradation impedes economic and social development and diminishes human welfare.’ Thus the true cost of indiscriminate discharges to the marine environment are now beginning to be considered.
Control of marine pollution problems does not necessarily require sophisticated regulation but rather rigorous and eﬀective planning control that assigns an appropriate value to the marine environment. It also implies controls not only of direct discharges to the marine environment, but also throughout the river catchment draining to the marine environment and of atmospheric sources upwind.
Thus several areas of real concern in terms of potential marine pollution problems can be identiﬁed, although the evidence for large-scale eﬀects in the open ocean is modest. The oceans have a very large capacity to dilute and degrade wastes. Marine pollution problems are most evident where this capacity is not eﬀective, such as in coastal areas with restricted circulation or for contaminants that ﬂoat, such as oil or plastics. The assessment of the nature of these threats has changed somewhat over the years as we have come to understand the marine system better and also to regulate human discharges into the system. Indeed, in a recent report GESAMP noted: ‘While the resolution of these issues is neither simple nor easy, in most cases the nature of the ocean’s environmental problems is understood, the knowledge to solve them is available and the necessary management tools exist. What is lacking is the determination and political will to act’ (Huber 1999).
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