South Africa is the largest user of pesticides in sub-Saharan Africa and many studies have highlighted the occurrence
of pesticides in water resources. Poor management of water treatment facilities in combination with a relatively
high dependency on untreated water from boreholes and rivers creates the potential for exposure of
human communities to pesticides and their associated health effects. Pesticide use, physicochemical and toxicity
data was therefore used to prioritize pesticides in terms of their potential risk to human health. After eliminating
pesticides used in very low quantities, four indices were used to prioritize active ingredients applied in excess of
1000kg per annum; the quantity index (QI) which ranked pesticides in terms of the quantity of their use; the toxicity
potential index (TP) which ranked pesticides according to scores derived for their potential to cause five
health effects (endocrine disruption, carcinogenicity, teratogenicity, mutagenicity and neurotoxicity); hazard potential
index (HP) which multiplied the TP by an exposure potential score determined by the GUS index for each
pesticide (to provide an indication of environmental hazard); and weighted hazard potential (WHP), which multiplied
the HP for a pesticide by the ratio of its use to the total use of all pesticides in the country. The top 25 pesticides
occurring in each of these indices were identified as priority pesticides, resulting in a combined total of 69
priority pesticides. A principal component analysis identified the indices that were most important in determining
why a specific pesticide was included in the final priority list. As crop specific application pesticide use data
was available it was possible to identify crops to which priority pesticides were applied to. Furthermore it was
possible to prioritize crops in terms of the specific pesticide applied to the crop (by expressing the WHP as a
ratio of the total amount of pesticide applied to the crop to the total use of all pesticides applied in the country).
This allows for an improved spatial assessment of the use of priority pesticides. The methodology applied here
provides a first level of basic, important information that can be used to develop monitoring programmes, identify
priority areas for management interventions and to investigate optimal mitigation strategies