Soil contamination and persistence of pollutants following organophosphate sprays and explosions to control red-billed quelea (Quelea quelea).

Background: Red-billed quelea (Quelea quelea) are controlled at breeding colonies and roosts by organophosphate sprays or explosions. Contamination with organophosphates after sprays and with petroleum products and phthalates after explosions was assessed.

Results: Concentrations in soil of the organophosphate fenthion the day after sprays were uneven (0-29.5 µg g(-1)), which was attributable to excess depositions at vehicle turning points, incorrect positioning of nozzles and poor equipment maintenance. A laboratory study using field-collected samples provided an estimate of 47 days for the half-life of fenthion. After sprays, fenthion persisted in soil for up to 188 days. High concentrations were detected 5 months after negative results at the same sites, providing indirect evidence of leaching. Concentrations of total petroleum hydrocarbons (TPHs) and phthalates ranged from 0.05 to 130.81 (mean 18.69) µg g(-1) and from 0 to 1.62 (mean 0.55) µg g(-1) respectively in the craters formed by the explosions, but declined to means of 0.753 and 0.027 µg g(-1) at 10 m away. One year after an explosion, mean TPHs of 0.865 and mean phthalates of 0.609 were detected.

Conclusion: Localisation of high concentrations of fenthion likely to have effects on soil biota could be mitigated by improved spray management. Given a half-life in the soil of 47 days for fenthion and the possibility of its leaching months after applications raises concerns about its acceptability. The pollutants left behind after explosions have been quantified for the first time, and, given their long-term persistence, their continued use poses a threat to environmental health.