Bioavailability, Average Daily Dose and Risk of Heavy Metals in Soils from Children Playgrounds Within Owerri, Imo State, Nigeria

Abstract

Nine public school playgrounds across Owerri metropolis were investigated for metal fractions for three years (2012, 2013 and 2014) in order to assess bioavailability, average daily dose (ADD) and risk assessment code (RAC) of five heavy metals. A six steps sequential extraction procedure was used to quantify metal fractions with A ANALYST 400 Perkin Elmer AAS. Data of metal concentration was subjected to models and results revealed interesting information that could aid in decision making concerning children playground safety. Significant (p > 0.05) amounts of Zn, Co and Cu were found in the bioavailable fractions in all playgrounds for both seasons. Mean Percent bioavailability in 2012 ranged from Co (9.4) to Zn (28.11) though maximum bioavailability was observed for Mn (55) and minimum for Cu (3). In 2013 bioavailability ranged from Zn (36) to Ni (40.2) while maximum bioavailability was observed for Cu (69) and minimum for Mn (20). In 2014 it ranged from Co (58.6) to Mn (61.1) with maximum bioavailability for Cu (80) and minimum for Cu (21). Bioavailability of these metals in dry and rainy seasons followed the order; Zn > Ni > Cu > Mn > Co. Categorizing bioavailability the order was Residual > Non-bioavailable > Bioavailable. Average daily dose (ADD) showed that exposure to metal-contaminated soil by ingestion were most prominent for Zn and Mn but high ADD values were recorded in 2014 with Zn (1583.7 mg/Kg/day) as the highest. In 2012, values of RAC showed that only Zn (50) at CSO was high whereas almost all playgrounds showed RAC above 50. There was a general increase in RAC from 2012 to 2014. Thus, these metals may be readily bioavailable to children and in the long run constitute health problems for children who use these playgrounds regularly.