Agrochemical pollutants

Pesticides and fertilizers are widely used in agriculture. They are essential to the production of food and fiber for a growing world population, but they become pollutants when they damage nontarget organisms. Some herbicides are also applied directly to water to control aquatic plants and algae. Pesticides include a vast array of herbicides, insecticides, fungicides, and nematicides and are widely variable in chemical structure, benefit, and impact. Nontarget organisms include people who may consume contaminated food or water; adjacent crops damaged by spray drift; bees and wildlife; subsequent crops in rotation with the target crop; and aquatic life in rivers, lakes, and estuarine and coastal waters, where sea grasses and coral are particularly vulnerable. The agricultural use of pesticides and their impact on human health through spray contact, food, and drinking water has been extensively covered in the literature, so this review focuses on the risk of other environmental impacts and opportunities for risk reduction or avoidance. The risk to nontarget organisms from pesticides depends on the extent of use, inherent toxicity (acute and chronic), transport away from the site of application, persistence, adsorption by suspended material, and concentration-time patterns of exposure that are affected by dilution and hydrology. Bioaccumulation in the food chain has led to the banning of chlorinated hydrocarbon insecticides in most countries of the world. Fertilizers include nitrogen (N) and phosphorus (P), which are applied to agricultural crops with substantial benefits for increased yield, but also with impacts on the aquatic environment through leaching of nitrogen compounds and soil erosion of adsorbed phosphates. Consequences of nutrient enrichment (eutrophication) include algal blooms that disrupt aquatic ecology and compromise the utility of the water through the production of taints and toxins. Toxic heavy metals have also been associated with fertilizer application. Opportunities for reduction of risk include effective registration procedures, restriction or regulation of use, sewage and storm-water effluent treatment, interception of agricultural pollutant source (e.g., by riparian strips), and treatment to remove pollutants prior to use. Major challenges include the difficulties of isolating the effects of agrochemical fertilizers from other pollutant sources such as sewage and animal effluents, complexities of relating land use to water quality and river condition, and costs of measuring trace amounts of chemicals. Ecotoxicology is the science of measuring the acute and chronic response of aquatic organism to pollutants. Interpretation is complicated by the synergistic effects of cocktails of pollutants, and by interaction with stressors such as salinity, temperature extremes, and turbidity. The review concludes with a section on achieving sustainability through changes in agricultural practice and use of catchment-scale approaches.