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.

Effects of the organophosphate fenthion for control of the red-billed quelea Quelea quelea on cholinesterase and haemoglobin concentrations in the blood of target and non-target birds.

The red-billed quelea bird Quelea quelea is one of sub-Saharan Africa's most damaging pests, attacking small-grain crops throughout semi-arid zones. It is routinely controlled by spraying its breeding colonies and roosts with organophosphate pesticides, actions often associated with detrimental effects on non-target organisms. Attributions of mortality and morbidity of non-targets to the sprays are difficult to confirm unequivocally but can be achieved by assessing depressions in cholinesterase activities since these are reduced by exposure to organophosphates. Here we report on surveys of birds caught before and after sprays that were examined for their blood cholinesterase activities to assess the extent to which these became depressed. Blood samples from birds were taken before and after sprays with fenthion against red-billed quelea in colonies or roosts, and at other unsprayed sites, in Botswana and Tanzania and analysed for levels of haemoglobin (Hb) and activities of whole blood acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Background activities of AChE, BChE and Hb concentrations varied with bird species, subspecies, mass, age and gender. Contrary to expectation, since avian erythrocytes are often reported to lack cholinesterases, acetylcholinesterase activities in pre-spray samples of adult birds were positively correlated with Hb concentrations. When these factors were taken into account there were highly significant declines (P < 0.0001) in AChE and BChE and increases in Hb after contact with fenthion in both target and non-target birds. BChE generally declined further (up to 87 % depression) from baseline levels than AChE (up to 83 % depression) but did so at a slower rate in a sample of quelea nestlings. Baseline activities of AChE and BChE and levels of Hb were higher in the East African subspecies of the red-billed quelea Q. q. aethiopica than in the southern African subspecies Q. q. lathamii, with the exception of BChE activities for adult males which were equivalent.