TOXICITY - A measure of how poinsinous a substance is, usually caused by enzyme inhibitation. For example, Carbon Monoxide will bind with haemoglobin in the blood and prevent it carrying oxygen. For exapmle, DDT prevents normal passage of nerve impulses betwen nerve cells by inhibiting enzyme action. Not all pollutants are toxic - many harm indirectly.
SPECIFICITY - A measure of the differening toxicities of a substance on different organisms. A specific substance may be extremely toxic to one animal but not to another. For example, Pyrethroid insecticides will kill insects and mammals, but insects are more sensitive than mammals. When farmers use this insecticide they will use a dose that is harmfull to insects but not mammals.
PERSISTENT - A meausre of the rate at which a material breaks down and therefore the length of time it remains in the environment. Persistence is only applied to a substance that will eventually break down. For exapmle, CFCs, they are chemically stable and break down slowly so they remain in the atmosphere for decades. For example, Sewage effluent is not persitent because it breaks down rapidly as long as the conditions are right for decomposition to occur - warm, wet and plenty of oxygen.
BIOACCUMULATION - The increase in concentration of a substance in living tissue. Pollutants that can bioaccumulate: organochlorine insecticides, mercury and lead.
BIOMAGNIFICATION - The progressive bioaccumulation of a material along a food chain. Pollutants that bioaccumluate and are stored may be ingested by the organisms in the next trophic level where they may also store it. Over a period of time the concentration will increase as more small doses are added.
MOBILITY - A measure of how easily a material moves into the environment. More mobile pollutants are more likely to travel futher and cause issues over a larger area. Sometimes thay can become diluted and less harmful. For example, CFCs are persistent gases which are therefore not very soluble in water, meaning that during rainfall they are not removed.
SOLUBILITY - The ease with which the molecules of a material seperate and disperse into a liquid. Liposolubility is a measure of how easily a substance dissolves in fats and oils. For example, organochloine insecticides, lead, mercury. They can be stored inside living organisms for a long time.
BIODEGRADABILITY - Degradation is the chemical breakdown of a material.Biodegradation is the process of being broken down by biological processes, especially the action of decomposers such as bacteria. The rate of biodegradation is usually affected by temerpature and the availability of oxygen. For example: sewage, paper and cardboard. Less biodegradable pollutants include plastics and DDT.
SYNERGISM - The process where the presence of two materials produces a greater effect than the sum of their individual effects. For exapmle, oxides of nitrogen and sulphur dioxide (A+B) > (A) + (B).
MUTAGENICITY - A mutagen is a material that can cause changes to the DNA structure. For example, if a sperm or egg cell is affects that any baby produced may have abnormaliites that could be passed on. Mutagenic pollutants include Dioxins, ionising radiation and asbestos.
CARCINOGENICITY - A mutagen that causes body cells to start to multiply in an uncontrolled way. For example: abestos, DDT and cadmium.
TERATOGENICITY - A substance that interfers with gene function in a grwoing embryo so it causes non-inherited birth abnormalities.
PRIMARY POLLUTANT - A pollutant released by hukman activities, for example, carbon dioxide release when burning fossil fuels.
SECONDARY POLLUTANT - A pollutant produced by chemical reactions involving primary pollutants. for example, tropospheric ozone is produced by interaction with oxides of nitrogen from fuel combustion and oxygen in the atmosphere. The nitrogen dioxide is broken down by UV-A sinlight: This is a photo chemical reaction. The monattomic oxygen reacts with the diatomic oxygen to produce ozone.
NO2 ----------UV-A---------> NO + O.
O + O2 -----> O3.
POINT AND DIFFUSE SOURCES
Some pollutants are released by a small number of easily identifyable sources such as power stations - POINT SOURCES. It is easy to see the effect as they will occur mainly around the source.
Other pollutants are relesed from a large number of smaller sources such as vehicle engines - DIFFUSE SOURCE. The effects may be harder to judge as they generally sprea and are difficult to link to any particular source.
DIRECT AND INDIRECT EFFECTS OF POLLUTANTS
Some pollutants cause harm by having a direct effect on the envirnoment:
- Acid rain damages leaf cuticles.
- Crude oil kills sea birds.
Some pollutants cause harm to organisms by changing other features of the environment such that survival rates are reduced:
- CFCs are not toxic but they release chlorine into the stratosphere, leading to ozone depletion and this allows more UV light to reachthe Earth's surface. This can cause DNA damage.