Exploring Magnetic Properties as a Potential Pollution Proxy for Monitoring Levels and Bioaccessibility of Lead (Pb) in Playground Sand: a Preliminary Study

The need to control soil/dust quality in recreation sites of urban agglomerations, especially in those where children are exposed, has been extensively highlighted. Particularly, in children’s play sites it is imperative to quantify the levels of potential harmful elements (PHEs) in soils and dusts. Particularly, lead (Pb) is an element of concern since exposure of children to Pb and the consequently elevated blood Pb levels are linked to severe behavioral disorders and reductions of intellectual function. On the other hand, the use of magnetic methods is proposed as a quick and inexpensive first step in assessing soil/dust pollution by providing qualitative data on its degree and extent. The aim of the present study was to perform magnetic measurements in order to find a relationship between levels and bioaccessibility of Pb in playground sands and sand-bound iron-bearing magnetic phases. For this reason, composite sand samples were collected within the top layer at 37 public playgrounds in the broader area of the city of Thessaloniki, Northern Greece. Sampling conducted from 2-5 spots of the playground not covered by the treetops, nor at the edge of the playground or near to vegetation or urban furniture. The mass specific magnetic susceptibility (χ_lf) of the playground sands exhibited a range of 51-248.7 x 10^-8 m³ kg^-1 with a median of 149.8 x10^-8 m³ kg^-1 indicating a notable amount of sand-bound Fe-bearing magnetic phases. The frequency dependent magnetic susceptibility (χ_fd) varied among 0.11 to 7.73% with only limited sand samples exhibiting values >5%, suggesting the lack of super paramagnetic magnetite grains within the majority of the studied samples. The total Pb concentrations in playground sands ranged from 18.6 to 46.7 mg kg^-1 with a median of  28.7 mg kg^-1 and lies within the ranges reported by other researchers. Despite the insignificant differences observed on Pb contents among a sub-set of 12 sands with elevated χ_lf values (mean Pb 31.3 mg kg^-1 , χ_lf > 175 x 10^-8 m³ kg^-1 ) and the rest of the samples (mean Pb 29.7 mg kg^-1), a moderate correlation coefficient (r=0.685, p<0.05) was recorded between χ_lf and Pb in the enhanced magnetized sub-set underscoring a probable linkage with the ferrimagnetic particles of playground sand. Bioaccessible Pb concentrations (gastric phase) ranged from 5.73 to 20.7 mg kg^-1 with 22-44% of Pb being in  bioaccessible form in the playground sands. Different lead intake scenarios (based on bioaccessible Pb) underscored no health risk for children through sand ingestion with the exception of a worst case scenario of pica behaviour (intake 20g/d).

Acknowledgements: This research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme «Human Resources Development, Education and Lifelong Learning» in the context of the project “Reinforcement of Postdoctoral Researchers - 2^nd Cycle” (MIS-5033021), implemented by the State Scholarships Foundation (ΙΚΥ).