eath rate, but this is almost impossible. If a pollutant then the growth rate of an organism can be seriously affects any of the variables in this equation affected which can in turn affect the entire ecosystem (Freeman, 122).Now using the approach of classical toxicology we study the poisoning effects of chemicals on individual animals resulting in lethal or sublethal effects. Effects on individuals may range from rapid death (lethal) through sublethal effects to no effects at all. The most obvious effect of exposure to a pollutant is rapid death and it is common practice to assess this type of toxicity by the LD50 (the lethal dose for 50% of test animals) values, scientist can judge the relative toxicity of two chemicals. For example, a chemical with an LD50 of 200 milligrams per kilogram of body weight is half as toxic as one with an LD50 the more toxic a chemical. Death is rarely instantaneous, and even cyanide takes at least some tens of seconds to kill a human being.Perkins (1979) suggests that a sublethal exposure kills at most only a small proportion of a population, but the possibility that s sublethal exposure could cause a small proportion of individuals to die from acute toxicity seems self contradictory (Freedman, 126). For both the sake of this assignment and for practical purposes, it would be incautious to suppose that a sublethal exposure that affects individual organisms adversely is not close to that which will affect the population. There is no good reason to suppose that there is a constant relationship for different pollutants or different species, between the dose needed to kill and that needed to impair an organism. Therefore, given the difficulties of studying an ecosystem, the most effective way to predict biological effects is likely to be by discerning the least exposure that produces a deleterious response in individual organisms (Moriarty, 1960) and then examining the extent to which different environmental...
