lead to a non-sustainable situation, but the time lag may be very long (up to thousands of years). For the risk ratios, however, emissions to non-agricultural soil make a contribution of only about 10 per cent and are thus not a major source, even in the steady-state situation.
Figure 30.2 shows the risk ratios for human toxicity and aquatic and terrestrial ecotox-icity. Acceptable daily intake (ADI) values defined by the WHO and tolerable daily intake (TDI) values similarly defined by Vermeire et al. (1991) and Cleven et al. (1992) have been applied in calculating the risk ratio for human toxicity. For human toxicity the risk ratio of lead is already above 1 for 1990 and the risk ratio for the steady-state situation is above 1 for lead, zinc and copper, in decreasing order of magnitude.
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