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Main pollutants

The following types of water pollution are usually distinguished:

  • pollution by organic materials,
  • suspended solids,
  • pollution by nitrogenous materials and phosphorus,
  • mineral pollution by salts (chlorides and sulphates),
  • pollution by metals,
  • organic (micro-) pollutants, (more or less) toxic, for the drinking water supply or aquatic life: organochlorine products, benzene-toluene-xylene and their derivatives, Polycyclic Aromatic Hydrocarbons, pesticides etc.
  • radio-elements,
  • physical-chemical pollution: thermal pollution (hot water discharge), change in the pH or colour of the water.

In the industrial sector, the reduction in organic material discharge, particularly characteristic of the chemical, paper, textile and food processing sectors, was initiated in the 1970s with reductions at source combined with the implementation, made compulsory by legislation, of efficient wastewater treatment plants. Average treatment rates now reach 70 to 80%. These plants treat nitrogen and phosphorus more and more often.

The drop in industrial discharge has been more significant than that of household discharge in terms of organic, nitrogenous or phosphorus pollution.
The reduction in metal discharge (chemical, metallurgy, surface treatment sectors etc.) was launched on an incentive and regulatory basis in the 1980s (for example ministerial order of September 1985 on surface treatments).
Considerable progress has been made, although not as much as that achieved for organic materials.

Since the 90s, attention has also been on organic micro- pollutants, discharged in small amounts, sometimes difficult to detect and treat.

Actions are also undertaken with regard to livestock farms which, due to animal manure, generate organic material, nitrogenous material and phosphorus discharge likely to contaminate surface and underground water in intensive farming areas. Thus, the land spreading of animal manure is currently strictly regulated. It must notably meet fertilisation balance objectives (balance of the addition in relation to plant requirements). Slurry treatment units are also used in large livestock farms.

Physical-chemical pollution is also monitored and limited: limitation in the pH of the discharge, discharge temperature, progressive standardisation of the closed circuit for cooling water.

In the years to come, in light of European directives, the reduction in hazardous substances discharge (metallic and organic) – or even elimination in certain cases – will become a priority.

Underground water is even more fragile than surface water: located in a more confined environment, the renewal of groundwater tables is much slower than that of surface water (in particular deep water tables). Their degradation is therefore almost irreversible. This is why discharge into underground water has long been prohibited, unless in extremely exceptional cases.
The prevention of pollution likely to affect underground water, by chronic or accidental leakage/discharge is subject to specific and stringent requirements within the legislation: retention of storage and handling areas to repair leaks, monitoring of the state of water tables for the installations using pollutants (Order of 2 February 1998). Similarly, the treatment policy for contaminated sites aims at analysing, then limiting or eliminating the impact on underground water.

Pollution in the aquatic environment can have direct or indirect effects on human health as well as the environment.
Direct effects on human health can be caused by the high toxicity of the pollutants discharged into sensitive aquatic milieus (drinking water supply resources, bathing water): this is true of certain metals (mercury, chromium, lead, cadmium, nickel), nitrates or pesticides for example.
Indirect effects on human health relate to the contamination of the aquatic milieus by pollutants which are only slightly biodegradable and which can accumulate in certain compartments of the ecosystem (sediments, suspended solids) and, more importantly, can subsequently concentrate in living organisms throughout the food chain. These are found in metal pollution, plant protection products, polycyclic aromatic hydrocarbons (PAHs). These phenomena occur in small-scale pollution developing over a long period of time or accumulating in large catchment areas.
Finally, pollution in aquatic milieus can have consequences on the ecological quality of the milieus themselves:

  • by asphyxia due to high turbidity or the consumption of oxygen dissolved by an excessive biodegradable pollution load;
  • by eutrophication due to an excessive amount of nutrients (nitrogenous or phosphorus pollution);
  • by direct toxicity for the fauna or flora of the environment (nitrites, ammonia, insecticides, hydrocarbons, acid or basic discharge). 2Effects on man and the environment2 Suspended solids:
    Increased turbidity is detrimental to photosynthesis, fish respiration and clogs the aquatic environment. Particles can carry different forms of pollution (organic, metallic etc.)

Organic pollution:
Environmental asphyxia by consumption of the dissolved oxygen. Toxicity of the organic load which is only slightly biodegradable.

Nitrogen, Phosphorus:
Eutrophication of the aquatic environment by an excessive amount of nutrients for aquatic plants (algae) leading to environmental asphyxia. Toxicity of ammonia and nitrites for aquatic wildlife.
Nitrates can cause blood poisoning in infants by blocking the oxygenating haemoglobin.

Most metallic elements are essential to animal and plant life (trace elements). However, in high doses, they can be highly toxic. Metallic pollution in the aquatic environment poses a specific problem as it is not biodegradable. It tends to concentrate in living organisms (bioaccumulation or biomagnification).
Toxicological effects vary depending on the metal and its chemical form: organic compounds are generally more toxic. Generally speaking, the most frequently observed disorders are respiratory, digestive, nervous or cutaneous. Certain metals are also considered carcinogenic: Arsenic, Nickel, Chromium VI.

Extremely [1] hazardous substances [2] for the aquatic environment:
Insecticides are generally the most toxic pesticides. They are persistent organic pollutants undergoing three types of processes (transformation, retention, transport) depending on their pysical-chemical properties.
They are adsorbed into suspended solids and accumulate in certain compartments (sediments, organic materials, food chain). Depending on their chemical forms and properties, these substances have toxic, mutagenic and carcinogenic effects.

[1] List I of directive 76/464/CEE and appendix X of the water framework directive 2000/60/CE list a total of 42 substances considered highly hazardous for the aquatic environment: 4 heavy metals (Hg, Cd, Ni, Pb), the PAH category and 3 individual PAHs, 7 halogenated volatile organic compounds (HVOC), 6 other organohalogens including 4 chlorobenzene, 10 pesticides, 4 drines and 7 other compounds.

[2] The substances listed in appendices Va,b,c of the order of 2 February 1998 are considered hazardous for the aquatic environment. Organochlorine and organophosphorus pesticides constitute the majority of the substances concerned. These are mostly insecticides. Arsenic and its mineral compounds, PCBs (polychlorinated biphenyls), tin organic salts, trifluralin and benzidin complete the list.