Assessment of toxic heavy metal loading in topsoil samples within the vicinity of a limestone quarry in South Western Nigeria

摘要

Loadingof Pb, Cd, Cr, Cu, Co, Mn, Ni, Zn,and Fe in topsoil samples(TS)collectedfromthe vicinity of limestone quarry in South Western Nigeriawas investigated. Thirty TS weresampledwithin ½ km radius from exploration area and 5 background samples from undeveloped area10 km away from thestudy area. Limestone rock samples(RK)were also analyzed for metals’ content. All samples were pretreated and leached with appropriate acid solutions for some properties.All leachates were analyzed withatomic absorption spectrophotomer(AAS)technique. Soil pH ranged from 6.65to8.23, sandfrom55.8to75.0%, siltfrom16.6to34.6%, clayfrom8.43to13.6%,and organic matterfrom0.97to4.84%,respectively. These properties compared withthose ofbackground samples. Rock samples (RK) showed high Fe and Mn enrichment. Metals levels (mg/kg) in TS with background levels in parenthesis ranged as follows: 11.5 to 27.7 (10.5) Pb, 0.28 to 3.18 (0.55) Cd, 12.1 to 17.4 (5.50) Cr, 80.6 to 55.8 (3.81) Cu, 8.93 to 23.5 (11.1) Co, 262 to 710 (637) Mn, 6.34 to 17.4 (6.10) Ni, 36.0 to 620 (24.4) Zn, and 6585 to 13440 (4563) Fe. The elevatedenrichmentsuggestsinfluence from exploration activities. Residual phase showed highest enrichment for all metals possibly, because of high sand content. Positive correlations were shown between all metals, except Mn and Cd that were negative. Geoaccumulation index rating showed 0 for Mn denoting uncontamination, while others ranged from 1 to 2 indicating moderate contamination.