environmental sciences research institute - University of Ulster

The effects of transboundary air pollution
The deposition of chemicals from the atmosphere on to the surface of the earth is less obvious than the emission of
chemicals in waste water, solid waste or as a result of accidents. We can see emissions from chimney stacks in power
stations and smelters and from the spraying of agrochemicals but the chemicals are deposited onto land and water many
tens to hundreds of kilometres away and this is less noticeable. When these emissions cross national boundaries, this is
called transboundary air pollution and the chemicals involved are carbon, sulphur, nitrogen, heavy metals and persistent
organic pollutants (POPs).
The heavy metals that are subject to transboundary air pollution are mercury, cadmium, lead, arsenic and zinc and the
groups of POPs are the organochlorine pesticides (OCs), polychlorinated biphyenyls (PCBs) and polycyclic aromatic
hydrocarbons (PAHs) and because emissions in one country can affect the quality of the environment in another these
chemicals are regulated by international treaty. The United Nations Economic Commission for Europe has five such
treaties and the Convention on Long-range Transboundary Air Pollution is the main way that emissions and effects of
transboundary air pollutants are managed; the 1998 Protocol on Heavy Metals and 1998 Protocol on Persistent Organic
Pollutants (POPs) are concerned with heavy metals and POPs.
The Department for the Environment and Rural Affairs (DEFRA) is responsible for implementing the Convention on
Long-range Transboundary Air Pollution in the United Kingdom and they funded an investigation into the risks to lakes
from heavy metals and POPs deposited from the atmosphere. As most of these pollutants are concentrated in lake
sediments, they were the focus of the investigation. The work was published in 2007 (Rippey et al. 2007). The PhD
of Sarah Travers increased the reliability of the assessment, by doubling the number of lakes involved, and providing
independent evidence on the relevance of one of the toxicity tests used.
The Tier I risk assessment was completed as follows. Eighteen lakes that covered the range of contamination by heavy
metals and POPs deposited from the atmosphere in the United Kingdom and Ireland were selected (Fig. 1, previous page)
and samples of the sediment retrieved. The concentrations of seven heavy metals and three groups of POPs, OCs, PCBs
and PAHs, were determined and three sediment toxicity tests completed. The toxicity tests were reproduction and
survival with Daphnia magna, growth and emergence with Chironomus riparius and growth and survival with Gammarus
pulex (Fig. 2). The first two species are well established in sediment toxicity tests, but the latter much less so. Although
there was evidence that Gammarus should be particularly sensitive to heavy metals, Sarah showed that this is not the
case and that the Chironomus riparius test is the most relevant and efficient way of establishing sediment toxicity.
Figure 2. Sediment
toxicity tests.
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