Toxicological Risk Assessment of Lead (Pb) Contamination in Public Water System in Lagos Metropolis, Nigeria

Abstract

Study Background: Lead continues to be a significant public health problem in developing countries, where there are considerable variations in the sources and pathways of exposure. Aim: This study investigates the level of lead in drinking water sources in Shomolu, Yaba and Bariga areas of Lagos State, Nigeria and the human risk exposure using a mice model. Materials and Methods: Water samples were collected in public water sources (borehole, sachet water, bottle water and tap water) and analyzed for lead using Flame Atomic Absorption Spectrophotometer (Varian model-AA240FS) equipped with a lead hollow cathode lamp. Contamination factor was determined. Healthy Mature female albino-mice, weighing 25.3 ± 2.5 g were exposed to the contaminated drinking water for 28 days to the different concentrations of lead nitrate: 1 mg/l, 10 mg/l, 50 mg/l, 500 mg/l and 1000 mg/l. Blood and liver were collected for hematology liver function test and histopathology. Results: Lead concentrations in public water sources in Shomolu, Bariga and Yaba areas of Lagos State were below 5.0 μg/l and contamination factor were less than 1.0. At 1.0 mg/l (1000 μg/l) Lead exposure, the relative weight increase in this group (as compared to the controlled group) was very slow, up to the 14th day (with weight loss of 3.17 g and relative weight loss of 23.1%), then increased up to the 28th day (with weight loss of 7.34 g, and relative weight gain of 18.4%). At 50.0 mg/l Lead exposure, there was a rapid weight decrease, a greater relative weight loss was experienced at the 14th day (weight gain, 1.36 g and 67.0% relative weight loss), then there was weight recovery at the 28th day (weight gain of 4.60 g, 25.8% relative weight loss). The 100.0 mg/l Lead exposed group showed steady decrease in weight, 14th day had a weight gain of 2.02 g and relative weight loss of 51.0% while the 28th day had 2.10 weight gain and 66.1% weight loss respectively. In the 500.0 mg/l Lead exposure group, a similar trend was observed as with 1.0 mg/l and 50 mg/l Lead exposures, showing greater weight loss at the 14th day (2.14 g and 151.9% weight loss), as compared to the 28th day exposure (1.36 g and 121.9% weight loss respectively). Alanine aminotransferase (ALT) and Akaline phosphatase (ALP) in the control group increased with time, but these had a different trend in the exposed groups. The RBC decreased with increase in concentrations from 1.0 mg·l to 50.0 mg/l Lead exposures, after which it increases at 100.0 mg/l, 500.0 mg/l and 1000 mg/l. The highest RBC was noticed at the highest exposure concentration at the 28th day with RBC, much higher than the control. The highest WBC was noticed at the highest exposure concentration at the 28th day with WBC, 8.77 ± 2.36 (×109/L) (p th day, 100.0 mg/L exposed mice’s liver had cellular vacuolization and mild necrosis. At 14th and 28th day of exposure, the 500.0 mg/L and 1000.0 mg/L exposed mice had significant liver pathological alterations including the presence of polymorphic nuclei, blood vessel congestion, cellular vacuolization and severe necrosis. Conclusion: Lead induces hematological disturbances, liver histological alterations and change in weight in mice. These become obvious as exposure concentration increases with time. Continuous monitoring of municipal water pipeline reticulation should be ensured to prevent incidence of seepage of toxicants such as lead into domestic water sources.