Pollution Indices of Heavy Metals in Urban Farm Soils along selected Highways in Lagos, Nigeria

Urban farm soil may be severely affected by heavy metal (HM) pollution, impairing environmental and human health. Proximity to pollution source such as roads can compromise soil quality, especially in ever-expanding cities with limited cropland. Pollution indices are useful tools for describing HM pollution of soils. Therefore, this study utilized pollution indices to assess HM pollution of urban farm soils along selected major highways in Lagos, Nigeria. Surface soil samples (0 –15 cm) were collected from the highway to the farms. Soil parameters (pH and organic carbon) and HMs (Cd, Cr, Co, Ni and Pb) were determined using standard methods and atomic absorption spectroscopy, respectively. Pollution indices: contamination factor (C), contamination degree (C ), f d geoaccumulation index (I ), pollution load index (PLI), ecological risk geo (E) and risk index (RI) were used to determine HM pollution. Soil pH r ranged from 5.36±0.34 – 6.97±0.24, indicating strongly acidic to neutral -1 state. Organic carbon was > 4% across the study area. Soil HM (mg kg soil) varied as follows: 1.30±1.06 to 7.76±5.65 (Cd), 2.85±0.49 to 29.54±17.25 (Ni), 0.08±0.07 to 1.53±1.65 (Cr) and 0.11±0.04 to 22.68±7.19 (Co), while Pb was generally very low. Only Cd exceeded the recommended limits. In terms of C , soils were moderately contaminated by Co (1.07) f but very highly contaminated by Cd (7.27). Mean C showed moderate d (8.34) contamination across the study sites, while mean PLI (0.42) suggested that most soils were unpolluted. Most of the I values for Cd geo Mots clés: Sol urbain; métal lourd; indices de pollution; Risque écologique were >1 indicating moderate pollution in soils. Moreover, soils had high to dangerous E by Cd (95.12 – 567.80) and the RI values showed r moderate to high risk in 50% of the study area. This urban farm soils showed relatively serious pollution with cadmium. There is the need to prevent and control sources of this heavy metal into the soil environment.