Past and Current Crimes

Some of the concern today is centred on problems inherited from less enlightened ages which will be with us for many years to come. Examples include spoil heaps from mining operations, contaminated land from previous industrial sites, and pesticides which are now banned but have such a long lifetime in the environment that they will continue to pollute for many decades. Current concerns include emissions from our automobiles, waste production, production of toxic particulate matter from combustion and incineration processes, use of pesticides which build up in the food chain and the use of inorganic fertilizers in agriculture. Although more environmentally friendly methods for power production are being introduced, there is still a large-scale reliance on fossil fuel for energy production with its inevitable production of carbon dioxide.

1.3 Pollution

All of us have concepts of what pollution is but have you considered how it may be defined?

What you would consider to be a definition of pollution?

Answer

The following definition is from the Organization of Economic Cooperation and Development:

'Pollution means the introduction by man, directly or indirectly, of substances or energy into the environment resulting in deleterious effects of such a nature as to endanger human health, harm living resources or interfere with amenities or other legitimate use of the environment.'

Before we concentrate on the chemical aspects of pollution, it is worth remembering that this is not the only form of pollution. Noise is an example of physical pollution. Simply adding water to a river at a different temperature to the ambient can effect life in the river. This is a form of thermal pollution. Pollution is, however, often associated with the introduction of chemical compounds into the environment. Popular opinion usually sees these as unnatural (and therefore harmful) substances. Perhaps one of the best known recent examples was the concern over the emission of chlorofluorocarbons (CFCs). These have been used in aerosol sprays and other applications. They are linked with the depletion of ozone in the stratosphere, which could lead to an increase in the intensity of harmful ultraviolet radiation from the sun reaching the earth's surface and increasing the incidence of skin cancer. Although the production of CFCs themselves is now banned in developed countries, the existing CFCs will take many years to be removed from the atmosphere and related ozone-depleting compounds (e.g. hydrochlorofluorocarbons, (HCFCs)) are still being manufactured. The effects on the ozone layer will therefore remain for many decades.

More frequently, problems occur by the release of substances into the environment which are naturally present, with the problem arising simply from an increase in concentration above the 'natural' levels. Carbon dioxide is a natural component of the atmosphere produced by the respiration of living organisms. The potential problem of global warming is primarily associated with an increase in its concentration in the atmosphere as a result of fuel combustion, together with a decrease in the world's forests which recycle the carbon. Increasing concentrations of a number of other naturally occurring gases, such as methane and nitrous oxide, add to the problem. Nitrates occur naturally as part of the constant cycling of nitrogen in the environment (see Figure 1.1). The over-use of fertilizers can, however, produce a build-up of nitrate in water courses which leads, first of all, to excessive plant growth, but ultimately to the death of all living species in the water. The process is known as eutrophication. Apart from nitrogen itself, all of these species in the nitrogen cycle have been shown to exhibit environmental problems if their concentration increases greatly above the 'natural' level in water or in the atmosphere. This is summarized in Table 1.1

You should be able to think of many pollution examples of your own. Try grouping the problems into different categories, for instance, whether the pollution is a global problem (e.g. ozone-depletion) or a more local issue (e.g. waste dumping). When you read the next chapter, which deals with the transport of

Table 1.1 Examples of problems caused by excessive concentrations of nitrogen species

Species Problem

N2O Contributes to the greenhouse effect and is a potential ozone-depleter

NH3 Highly poisonous to fish, particularly in its non-protonated form

NO2- Highly poisonous in water to animals

NO3- Contributes to eutrophication (excessive plant growth) in watercourses;

associated with 'blue-baby syndrome' which can cause fatalities in infants pollutants, you may find that you change your mind about some of the problems. Lead pollution, which has been associated with the retardation of intellectual development in children, is normally thought to be a highly localized problem. Increased lead concentrations in the environment, largely from the use of leaded petrol in cars, can be detected hundreds of kilometres from likely sources.

If a pollutant is discharged into the environment, what causes the effect on individual living organisms:

• the total amount discharged;

• its concentration in the environment?

Answer

It is the concentration which is of concern with respect to individual living organisms.

This statement may seem surprising but consider the following facts. All compounds are toxic at high enough concentrations. Even something apparently as innocuous as sodium chloride has adverse effects when present in high concentration. For example, you cannot drink more than a small quantity of sea water without being made ill. Some metals, which are necessary for plant growth when found in small concentrations in the soil, would kill the plant life when found in larger concentrations on, let us say, a waste dump. These include elements such as chromium, cobalt and manganese, and are often known as 'essential' elements.

Of course, if we are considering the effect of a particular pollutant on the global environment, we would have to consider the total quantity emitted. Excessive amounts would ultimately increase the background concentration, as is the case with carbon dioxide emissions.

It would then appear, that in order to limit the adverse effect of a particular ion or compound, it is necessary to ensure that the concentration in water or in the atmosphere is maintained below a pre-determined 'safe' level. As will be shown in the next section, the establishment of such levels is fraught with difficulty. Nonetheless, much of the world's environmental legislation is drafted in terms of specifying maximum concentration of ions and compounds (Table 1.2).

Table 1.2 Extract from European Community Directive 80/778/EEC relating to the quality of water intended for human consumption - parameters concerning substances undesirable in excessive amounts3. Reproduced by permission of the Official Journal of the European Communities

Parameter

Expression

Guide

Maximum

Comments

of the

level

admissible

results3

(GL)

concentration (MAC)

21 Nitrites NO2

22 Ammonium NH4

23 Kjeldahl nitrogen N (mg l-1) (excluding N in

NO2 and NO3)

24 (KMnO4) oxidizability

25 Total organic carbon (TOC)

27 Substances extractable in chloroform

28 Dissolved or emulsified hydrocarbons (after extraction by petroleum ether); mineral oils

29 Phenols (phenol index)

Dry residue (mg l-1)

C6H5OH

30 Boron

31 Surfactants (reacting with methylene blue)

Measured when heated in acid medium The reason for any increase in the usual concentration must be investigated

Undetectable organoleptically

Excluding natural phenols which do not react with chlorine

1000

a Certain of these substances may even be toxic when present in very substantial quantities.

What are the maximum concentrations that the substances listed in Table 1.2 can be considered to be acceptable in drinking water?

Answer

These, of course, vary from substance to substance, but you should have noted that most of the maximum admissible concentrations are expressed in units of mg l-1 (sometimes called parts per million (ppm)), whereas others are expressed as fig l~l (or parts per billion (ppb)).

Was this article helpful?

0 0

Post a comment