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Detergents, phosphates and water quality

Your laundry and the environment

Each time a washing machine empties, water loaded with soil removed from the fabrics, and with the chemicals used in the detergent, is discharged into the sewer. Various measures are routinely used to assess the possible impact on the environment of a detergent formulation and its ingredients. These include toxicity to aquatic organisms - fish, invertebrates and algae; biodegradability; chemical and biological oxygen demand; suspended solids and so on.
The potential for environmental damage arising from detergents has steadily been reduced over many years due to three main factors:

  • advances in sewage treatment ensuring better removal or degradation of substances discharged to sewers, and the extension of sewage collection and treatment networks to a greater proportion of households;
  • in designing detergent formulations, manufacturers develop and use active ingredients which will be substantially removed or degraded by modern sewage treatment processes; thereby posing the minimum risk of environmental damage;
  • the development of high-performance, low-dosage detergent formulations helps to ensure that consumers keep environmental loading to the minimum whilst maintaining washing performance.

In each of these factors, the use of phosphate in detergents has an important part to play: it is highly effective as a builder, it minimises the use of other active ingredients, it is essentially non-toxic to aquatic organisms and it is cheaply and extensively removed from sewage treatment works using well established techniques. In addition, phosphate, alone amongst detergent ingredients, has the potential to be recovered and recycled from sewage treatment works - either as sludge for application as fertiliser for agricultural land or, using emerging techniques, as high grade products for industrial, detergent or even food and pharmaceutical use.
Whilst these benefits of phosphate-based detergents are widely recognised, it is the behaviour of phosphate as a nutrient and the question of its involvement in the process of "eutrophication" which is at the centre of a 20-year-long controversy.

What is eutrophication?

The term "eutrophication" has its origins in the Greek word "eutrophos", meaning well-nourished. But all-to-often, the term has come to be associated with adverse water quality.
Nutrient enrichment is a natural process. It is not unusual to find lakes and rivers which have become rich in the main nutrients including carbon, silicon, nitrogen and phosphorus by erosion or runoff from adjacent soils. These nutrients are essential for the growth of phytoplankton (algae) which are the first link of the food chain and, hence, the basis for all aquatic life. In surface waters and, in particular oceans, this primary production speeds the diffusion of carbon dioxide from the atmosphere to the oceans, the largest sink for carbon dioxide.
The food chain itself consists of many levels, each with complex interactions but, in the simples terms can be considered as follows: phytoplankton are consumed by zooplankton such as daphnia (water fleas) - the food for many species of small fish. These planktivorous fish are consumed by larger predatory fish which, together with their prey, are the food for birds and mammals and, indeed, man.
A healthy and well-nourished water body (river, lake or sea) sustains a rich and diverse aquatic life with all the layers in the food chain existing in a dynamic equilibrium of production and consumption. A healthy food chain can often show remarkable resilience to large changes in nutrient load or climatic conditions without showing any long term changes in water quality or species diversity.

However, the pressures of an expanding population, urbanisation, industrialisation and agricultural intensification in many regions have resulted in a massive increase in the loading of, not just nutrients into rivers, lakes and estuaries, but untreated or partially untreated sewage. Industrial discharges, pesticides, animal wastes and countless other pollutants have a direct and devastating effect on the functioning of the food chain.
The combination of greatly increased nutrient input and a wide range of other, potentially ecotoxic, inorganic and organic products which reach the water can have serious effects on the aquatic ecosystem. At the same time as primary production of algae is promoted by the increased nutrient supply, the ability of the zooplankton (usually the most pollution-sensitive organisms in the food chain) to respond to this increased food supply is impaired by the presence of other kinds of pollutants.
The result is often that the balance of production and consumption in the food chain is disturbed and, in most cases, this lead to algae becoming the dominant form of life in the water.
In the worst cases, algae proliferate in a way which is no longer controlled by higher levels in the food chain. This may lead to a decline in other water plants, particularly bottom growing plants which fail to compete for light in the turbid-water column. This loss in plant diversity can also led to a shift in fish species which may further affect the operating of the food chain. In the most extreme cases, toxic algal scums may be formed and water may become deoxygenated, leading to fish kills.

Unfortunately, the behaviour of water bodies when simultaneously subjected to large pollutant and nutrient loads is very hard to predict. It is possible to find many examples of lakes and reservoirs where elevated nutrient levels have not resulted in the water quality problems of high algal biomass, while similar lakes, with similar nutrient loads can exhibit signs of algal domination. This uncertainty in the effects of increasing, or for that matter decreasing nutrient levels raises particular problems for lake and reservoir management where it may be more important to consider the quality of water reaching the water body from more aspects than simply that of nutrients.

Sources of phosphorus input to the aquatic environment in the EC; phosphate from detergents represents a minor part of the total anthropogenic phosphorus input. In European rivers and lakes, their average contribution to the total release represents at most 10% of all sources, with the lowest value in Germany (3%) and the highest in the United Kingdom (19%).

Sources "The Economic and Environmental Impact of Phosphorus Removal from Wastewater in the European Community", Imperial College of Science, Technology and Medicine, 1993.

Algal growth and control

Within any aquatic ecosystem with a functioning food chain, two simultaneous mechanisms control algal abundance or biomass. These are generally known as bottom-up and top-down controls.

Bottom-up control

Algae, the first step in the food chain, need a number of factors to promote their growth. They need sunlight for photosynthesis; they need a certain degree of warmth (although the optimum climatic conditions vary from species to species, like flowers in a garden); they may need certain water conditions (turbulence) and they need nutrients. The most important of these are carbon, silicon (which is the key element in species of algae known as diatoms), nitrogen and phosphorus which, broadly speaking, are required in the ratio 100:50:10:1 respectively, but a huge range of trace elements is also necessary for algal development.
Given all these conditions, algae and many other water plants begin to grow and the water comes to life. This "primary production" is the foundation of the food chain upon which all higher life forms: invertebrates, fish, birds and mammals are sustained. Remove any of these essential conditions, and this primary production ceases and higher life forms can not be sustained.

Top-down control

Given an adequate level of algal production, a healthy food chain can develop in the aquatic environment. This food chain - algae, grazing zooplankton (invertebrates); planktivorous fish; piscivorous fish; birds and mammals - is built upon the foundation of primary production. In a healthy ecosystem, the ability of the food chain to adapt to variations in nutrient load can be quite remarkable. In its simplest sense, the water body is capable of sustaining a richer and more productive food chain. This can also be achieved without any deterioration in water quality. The availability of nutrients causes an increase of algal production but this is balanced by an increase in algal consumption by organisms higher in the food chain which prosper on the increased food supply. Such a situation can often be beneficial in supporting a productive sporting or commercial fishery, and wildlife.

Loss of control

There is much debate about what factors can be important in causing a loss of this top-down control in a water body. There is no doubt however, that under certain conditions, algae growth can exceed the ability of the ecosystem to maintain a natural balance, provoking consequences such as oxygen depletion, increased turbidity, and eventually the disappearance of competitive species such as rooted plants and animals.
Under these conditions, an imbalance develops between the rate of algal consumption and changes in the species composition. This may result in reduced biodiversity which is often difficult to reverse.
Conventionally, the approach to the restoration of such water bodies has been to try to limit algal production by reducing the supply of nutrients. Phosphorus is generally chosen as the nutrient to control because, unlike nitrogen, it can be relatively easily removed at the sewage treatment works and the main agricultural sources can often be identified and reduced by changing farming practices.
In general, this bottom-up approach to controlling algal density produces disappointing results. Whilst, phosphorus is the easiest nutrient to remove, it is also the one which is needed in the smallest quantity compared with the other primary nutrient, nitrogen. It can often be difficult to reduce all the sources of phosphorus input to an effective level and, even then, sediments can act as a significant, "reservoir" for phosphorus which can be released into the water column.

Furthermore, phosphorus control may be irrelevant in certain water bodies, particularly estuaries and the marine environment where silica and nitrogen would usually be expected to control primary production but where phosphorus in naturally abundant.
Where a food chain has become disturbed or discontinuous, algae tend to dominate and algal densities begin to rise. Many lake and reservoir restoration programmes now use a combination of bottom-up and top-down controls to bring about water quality improvement. A combined approach to limiting nutrient availability (and hence the scope for primary production) and techniques of bio-manipulation - aimed at restoring a healthy food chain - have generally produced much better and more sustainable results. The importance of good, overall sewage treatment and the prevention of the pollution from for example pesticides are also becoming more widely appreciated, as the potential role of toxins in the effectiveness of algal density regulation by the food chain becomes more apparent.

Research in the Netherlands, for example, has demonstrated that the amount of nutrients which could be added to unpolluted lake water before an increase in algal density was 2.5 times higher than for water taken from a polluted lake. This shows that when daphnids have their ability to consume algal biomass reduced by toxicants, the observed algal density rises in response and water quality problems are likely. It is important to note that the rate of algal production (i.e. the rate at which algae grow and reproduce) was similar in water from both lakes and that the difference was due to the efficiency of algal grazing and the health of the food chain.
Further studies on ecosystems polluted with small traces of toxic components showed an immediate reaction when nutrients were introduced. This resulted in a rapid rise on algal density and an inability of daphnids to feed on and regulate algal biomass due to a toxic anorexia effect.

Water pollution, algal density and the need for a global approach

Laboratory and field studies increasingly show that problems of algal density in water are not simply a function of nutrient availability. They are also strongly associated with other forms of pollution form metals, pesticides, inadequately treated sewage, etc.
The reversal of these adverse changes to water quality demands a global and comprehensive approach to improving water quality. Not only should the input of nutrients be reduced (through better standards of sewage treatment) but the input of pollutants from households and industry must similarly be reduced. In catchments where agriculture inputs are high, changes in agricultural practices might also be required.
At least as far as domestic sewage and some industrial effluents are concerned, improved sewage treatment techniques will often address both the nutrient and pollutant issues together.

Detergent phosphate bans and water quality

From the beginning of the restriction on detergent phosphates in the 70s, no study has ever shown any positive impact with respect to biomass concentration or improvement of water quality. The only observed effect in some areas was a partial reduction of phosphorus concentration in rivers.

On the other hand, studies conducted by three independent institutes showed that in 1987, the year after phosphate based detergents were banned in Switzerland, the total detergent consumption is this country increased by more than 15%.



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