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Lead levels in rivers, sediments and fish ponds in the Ibadan metropolitan area, south-west Nigeria

Lead levels in rivers, their surface sediments, and in fish ponds in Ibadan, Nigeria, were assessed in the 2003–2004 dry and wet seasons. It was planned to reduce lead levels in petrol, regarded as the major source of lead in the Nigerian environment, to 0.15g l−1 by the end of 2002 and to zero by 2004, while 2005 was to be the phase-out year for lead additives in petrol throughout the sub-Saharan region. The WHO-recommended limit for lead levels in surface water is 0.01mg l−1. Despite the now-reduced lead content in petrol, lead levels in surface waters ranged between 0.5–2.35mg l−1 (mean 0.76mg l−1) and 1.15–2.20mg l−1 (mean 1.34mg l−1) during the dry and rainy seasons, respectively. Lead levels in river sediments ranged between 0.9–4mg kg−1 (mean 1.86mg kg−1) and 1.15–2.2mg kg−1 (mean 1.49mg kgl−1) during the dry and rainy seasons, respectively. Lead levels in fish ponds were even higher, at 1.09–2.9mg l−1 (mean 1.88mg l−1). The present situation therefore indicates severe lead contamination of aquatic systems in Ibadan City, which portends a serious public health risk to humans. A detailed assessment of other sources of lead pollution in the Nigerian environment — besides vehicle emissions — is required if lead pollution is to be reduced effectively.