Abstract
D.Phil (Aquatic Health)
Pesticides have been used to control and eliminate agricultural pests for many years thereby increasing crop yield in agriculture; however, the increasing human population worldwide has put increased pressure on agriculture to produce food. This is especially true in developing countries where the population growth has exceeded the predicted growth. Agriculture has therefore become more reliant on pesticides to increase the crop yield to meet the food demand. Many of the pesticides that are used in developing countries are not well studied in these countries and only limited information on their effects on the local environment is known. The information that is available is often from temperate regions and the effects of the pesticides in more arid, subtropical areas are not known. This is especially true in South Africa where a limited amount of studies on pesticides and their effects on the environment have been completed. The problem developing countries (including South Africa) face is the lack of funding which limit the studies on pesticides. Thus, a method was developed in Sri Lanka and Thailand whereby the risk and effects of pesticides to the environment, specifically non-target organisms, can be estimated using an international database which contains predominantly temperate data of pesticides. The first time this model was tested in South Africa was on the Crocodile River (West) Irrigation Scheme in the North West province. This model is initially dependant on the input of information from local farmers on the usage of pesticides. The data were then combined with secondary data on the pesticide characteristics to establish a preliminary risk posed by the pesticides. This risk could then be validated through biological monitoring and the actual pesticide values measured in the environment. This current study was initiated to test these probabilistic models in another part of South Africa with a more arid climate. The Vaalharts Irrigation Scheme (VHIS) comprises an area of 40 000ha where intensive agriculture activities take place and pesticide use is evident. The water for the irrigation scheme is transferred from a weir in the Vaal River to various irrigation canals and dams downstream. Water is then pumped out of the dams to irrigate the various crops. The runoff and drainage water is routed to drainage canals that return to the Harts River. The main crops in the area are wheat, maize and groundnuts, and a wide range of pesticides are used from the time the crops are planted until they are ready to be harvested. The current study was based on the Crocodile (West) River study in terms of the methodology followed, to further validate the use of the risk assessment methodology in southern Africa. Based on a situation analysis of the study area the following two hypotheses were formulated: the predictive and integrated risk models can be used to assess the ecological risk of pesticides when applied on the VHIS; and the risk information generated with these models can be communicated in an effective manner by using a Decision Support System (DSS).