Heavy metal concentrations in roadside soil and the correlation with traffic in Malta

Abstract

Automobiles are a source of metal pollution. The burning of fossil fuel and the overall degradation of car parts, shed a considerable amount of metals into the air with a possibility that these end contaminating the soils in the vicinity of major road networks. This study aimed to identify how heavy metal concentrations in soil vary according to traffic on Maltese roads. Soil was sampled along a major road from three areas, Marsa, Hal Far and Gozo that have contrasting traffic density. Additionally, heavy metal concentrations from surrounding areas, distant from the main road but within the area, were also analysed in order to further compare and contrast potential contamination. Soil samples were processed using the digestion and AB-DTPA extraction methods, whereby identification of the total, and the available, heavy metals was achieved respectively. Traffic density information was obtained from Transport Malta [TM]. The main findings of this study suggest that the roadside soil sampled from Gozo as a region experiences overall lesser vehicle counts than Malta, hence potentially implying lesser concentrations of heavy metals emitted from vehicle combustion or frictional parts (brake, and tyre wear). On the other hand, Marsa roadside soil samples depict the highest exposure of heavy metals in soils. Furthermore, the Birżebbuġa roadside samples showed that this region is affected by traffic however not as heavily impacted as Marsa. Surrounding areas in the former i.e. Marsa region were also depicted as high, with the plausibility of having accumulated dispersal from neighbouring areas. In contrast, the other surrounding areas analysed, displayed lower concentration levels than their roadside samples. Lastly, the highest concentrations observed in descending order include Ba, Zn, Pb. Further research is recommended in order to obtain a more comprehensive view on this matter.