6 Self-assessment questions
Give three reasons why many people in the world face an increasingly severe shortage of fresh, safe water.
The human population of the world is increasing rapidly; per capita use of freshwater is increasing; climate change is altering the distribution of freshwater, making it more scarce in some regions, such as southern Africa. You might also have answered, correctly, that an increasing proportion of water supplies are polluted, by pathogens and by xenobiotic chemicals, as a result of increasing urbanisation and industrialisation.
In some parts of the world, people are advised to limit the amount of certain kinds of fish that they eat; why is this?
Large, predatory fish occupy a position at the top of food chains in which, by bioaccumulation, they can contain high levels of xenobiotic chemicals, such as methyl mercury, which may be harmful to human health, particularly during fetal development.
Describe how, as levels of nitrogen compounds increase in the environment, their effects on human health change.
At lower levels, nitrogen compounds cause deterioration, by eutrophication, of natural water bodies, which can promote the formation of algal blooms. This can have indirect effects on human health by depleting fish stocks on which some communites depend. At higher levels, they can have a direct impact on human health, for example, by causing ‘blue baby syndrome’ and also asthma in some localities.
What does it mean to say that a particular xenobiotic chemical is an endocrine disruptor?
An endocrine disruptor is a chemical compound which, though not itself a hormone, has a molecular structure that enables it to mimic the effect of a hormone in an animal. The commonest examples of endocrine disruptors are those that mimic female hormones and feminise male animals (e.g. fish).