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The indicator surface water toxicity
measures the potential impact of impaired water quality on people
and ecosystems. As toxicity is not measured as part of DWAF's
regular monitoring programme, toxicological data is only available
from specialist studies and specific licence compliance monitoring
programmes. A measure of toxicity is therefore derived from
comparing toxic water quality variables with guideline values and
results in a percentage exceedance of surface waters from both
drinking water guidelines and aquatic ecosystem
guidelines and thus giving an
indication of the potential toxicity of surface waters to human
health and
ecosystems.
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| Assessment of
Data |
Due to the lack of data on toxic variables,
water quality has been assessed on the basis of its "suitability for
use" by the industrial and irrigated agricultural sectors. South
African Drinking Water Quality Guidelines for use in these two
sectors were used as a guideline and percentages of samples
exceeding these guideline values was produced. Total Dissolved Solids
(TDS) in the Upper Vaal WMA are higher than the guideline values in
almost 40% of samples taken, and almost 33% of samples taken in in
the Usutu WMA exceeding the irrigation guidelines. The highest
exceedance rate was in the Olifants WMA with over half the samples
tested exceeding irrigation guidelines for
TDS.Other parameters worth noting, were:
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TDS levels in the Olifants WMA increased
since 1996, while in the Inkomati WMA is showing an increasing
trend, while the Usutu WMA has shown
a downward trend since 1996;
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67% of samples taken in the Usutu WMA
exceed irrigation guidelines for sulphate;
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74% of samples taken in the Upper Vaal
WMA
exceed irrigation guidelines for magnesium;
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65%
and 52% of samples taken in the Upper
Vaal and Olifants WMAs, respectively, exceed irrigation guidelines
for electrical conductivity (EC); and
-
over 50% of samples taken in the
Olifants WMA exceed industrial and / or irrigation guidelines for
pH, EC,
TDS aluminium, iron and manganese.
In terms of drinking water guidelines, the
Upper Vaal WMA has 40% or more samples exceeding the levels for TDS,
while the Olifants has 50% of samples exceeding the
levels for aluminium and manganese.
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