Effluent runoff from agricultural land use

The increasing level of nitrite found in the drinking water of Costa Rica's Central Valley is directly attributed to leaching into groundwater of agrochemicals used in surrounding coffee plantations. Excessive concentrations of nitrates and phosphates in surface waters and marine ecosystems are also observed. Nutrients were seeping up to the surface and mixing with the direct discharge of coffee residues and water used in pulping and washing coffee beans. This contamination manifested as noxious odours and unsightly debris, a depleted diversity of micro-organisms in and along riverbeds and, in extreme cases, fishkills from oxygen depletion and toxic byproducts of organic decomposition. Pesticide run-off from cocoa plantations in Brazil are also said to have caused fishkills and contamination of drinking water supplies. Furthermore, pesticide containers are often washed in running rivers before being reused for other purposes.