The potential for heavy metal pollution in crops from urban and peri urban horticultural farms in the Gaborone environs: a review

Abstract

The introduction of urban and peri-urban agriculture (UPA) is usually characterized by high input intensity. This intensive use of chemical fertilizers, pesticides, wastewater, sludges and industrial effluents may lead to accumulation of potentially toxic metals in the soil, increasing the geological background levels and exceeding the capacity to immobilize them. Besides being environmental pollutants of which the toxicity is a problem of increasing significance for ecological reasons, heavy metal accumulation in the food chain is highly dangerous for human health. The objective of this review was to highlight the potential problems that may arise as a consequence of irrigating crops with sewage water as well as using fertilizers and pesticides. A review of literature has shown that different types of fertilizers contain some quantities of heavy metals that may buildup in the soil as well as be taken up by crops. In addition to using fertilizers, the use of treated and sometimes partially treated and untreated water by UPA farmers around Gaborone may lead to heavy metal accumulation in soil as well as in crops, posing a danger to human beings. In Botswana there is limited information concerning heavy metal accumulation in soils even though there is a high use of agrochemicals in vegetable production in UPA land use systems. Lack of such information necessitates research on the impact of the application of fertilizer, sewage water (treated and untreated) and metal-based pesticides on the quality of the vegetable produce coming from UPA.