Clean waters | Organically polluted waters | Waters showing eutrophication | |
Producers | 80 | 15 | 87 |
Consumers | 13 | 5 | 4 |
Decomposers | 7 | 80 | 9 |
pH range | Effect |
---|---|
6.5–9.0 | No effect |
6.0–6.4 | Unlikely to be harmful except when carbon dioxide levels are very high (1000 mg l−1) |
5.0–5.9 | Not especially harmful except when carbon dioxide levels are high (20 mg l−1) or ferric ions are present |
4.5–4.9 | Harmful to the eggs of salmon and trout species (salmonids) and to adult fish when levels of calcium, sodium and chloride are low |
4.0–4.4 | Harmful to adult fish of many types that have not been progressively acclimated to low pH |
3.5–3.9 | Lethal to salmonids, although acclimated roach can survive for longer |
3.0–3.4 | Most fish are killed within hours at these levels |
Cholera | bacterium |
Poliomyelitis | virus |
Typhoid | bacterium |
Bilharzia | helminth |
Anthrax | bacterium |
Cryptosporidiosis | protozoan |
Organism type | Organism | Disease | Remarks |
---|---|---|---|
Bacteria | Vibrio cholerae | Cholera | Transmitted via sewage and polluted waters in cholera-endemic areas |
Salmonella typhi | Typhoid fever | Common in sewage | |
Salmonella paratyphi | Paratyphoid fever | Common in sewage | |
Salmonella spp. | Food poisoning | Cause of food poisoning; usually found in contaminated food of animal origin | |
Shigella spp. | Bacillary dysentery | Polluted waters are main source of infection | |
Bacillus anthracis | Anthrax | Can be found in effluents from tanneries processing hides from infected animals; spores resistant to treatment | |
Brucella spp. | Brucellosis (Malta fever) in humans; contagious abortion in sheep, goats and cattle | Normally transmitted by infected milk or by contact | |
Leptospira icterohaemorrhagiae | Leptospirosis (Weil’s disease) | Carried by sewer rats; also present in water contaminated by urine from infected animals and humans; can infect through cuts in skin, or intact skin if immersed for a long time | |
Viruses | Poliovirus | Poliomyelitis | Transmitted by faecal–oral route via contaminated food or water |
Hepatitis A virus (HAV) | Hepatitis A | Transmitted by faecal–oral route via contaminated food or water | |
Protozoa | Entamoeba histolytica | Amoebic dysentery | Spread by contaminated waters and sludge used as fertiliser; common in warm countries |
Giardia lamblia | Giardiasis | Found in inadequately treated water | |
Cryptosporidium spp. | Cryptosporidiosis | Carried by agricultural livestock and infected persons | |
Helminths | Taenia saginata | Tapeworms | Eggs very resistant, present in sewage sludge and sewage effluents; can be present in contaminated water sources and food |
Ascaris lumbricoides | Nematode worms | Present in sewage effluents and dried sludge used as fertiliser | |
Schistosoma haematobium, Schistosoma mansoni | Bilharzia | Carried by water snails in rivers and irrigation ditches contaminated by human waste in specific regions of the world; enter humans by direct penetration of skin |
Pollutant | General effect | Effect on biota | Effect on water supplies | Sources: natural | Sources: result of human activity |
---|---|---|---|---|---|
Organic (biodegradable wastes) | Increased oxygen demand; food provided for organisms lower down in food chain | Tolerated in moderate quantities if release not too quick, serious if dissolved oxygen (DO) drops too quickly | Increased need of treatment | Run-off and seepage through soil | Domestic sewage, food processing, animal wastes |
Plant nutrients | Excessive plant growth | Demand on DO | Increased need of treatment | Natural degradative processes | Animal wastes, fertilisers, detergents, industrial wastes |
Toxic chemicals (e.g. heavy metals, pesticides, phenols, PCBs) | Toxic to humans, animals and plants | Could be lethal | Increased need of treatment or control | Rare | Detergents, pesticides, tanneries, pharmaceuticals, wool scouring, refineries |
Endocrine disruptors | Alteration of ecology | May adversely affect health and reproduction of humans and animals | Can be present in water sold in plastic bottles | Fusarium species of fungus | Chemical manufacture, intensive farming |
Acids/alkalis | Lowering/raising of pH; acids can dissolve heavy metals | Only narrow range of pH tolerable for most plants and animals; heavy metals toxic | Corrosion | Naturally acid or alkaline rock | Battery, steel, chemical and textile manufacturing; coal mining |
Suspended solids | Reduction in light penetration (increased turbidity), blanketing, introduction of colour | Photosynthesis reduced; blanketing of benthic plants and animals; obstruction of gills of fish | Obstruction of filters; increased need of treatment | Soil erosion, storms, floods | Pulp mills, quarrying, any building or development work involving ground disturbance |
Immiscible liquids | Formation of a layer at the water surface that could prevent O2/CO2 interchange | Reduced DO; insect breeding affected | Interference with treatment processes | Unlikely | Oil-related activity |
Heat | Decrease in DO; increase in metabolic rate of aquatic organisms | Possible reduced breeding or growth of aquatic organisms | None | Unlikely | Power plants, steel mills |
Taste-, odour- and colour-forming compounds | Taste, malodour, colour | Tainting of fish | Increased need of treatment | Peat | Chemical manufacture or processing |
Microorganisms | Pathogenic to humans | None | Increased need of treatment | Animal excrement | Contamination from human wastes |