Long-term lead contamination and isotopic source identification in Northern Hungary

Lead is one of the extensively distributed PTEs (potentially toxic elements) in the environment due to wide-scale anthropogenic activities (e.g., mining, vehicular emissions, industries, etc.), its geochemical feature, and natural abundance. The World Health Organization (WHO) defined Pb as 2^nd most dangerous element for health, with particular concern for mental and physical disorders in adults and children. Salgótarján and Ózd cities (Northern Hungary) are two main former heavy industrial cities, with the smelter, steel industry, coal-fired power plant, coal mines, etc., supplied the country with coal and iron and steel products for centuries. The main aim of the research is to obtain a lead distribution map of the region and identify the potential sources by use of stable lead isotopes.

Urban soil samples were collected from each km² of both cities. Additionally, a soil as geochemical background, as well as local slag and coal as suspected major pollution sources were collected. Lead content and stable Pb isotopes of all samples were analyzed by ICP-MS spectrometry.

Obtained results indicate heterogeneous distribution and high lead enrichment in both cities, where the Pb concentration ranged from 8.5 to 1692 ppm in Salgótarján and from 6.6 to 1674 ppm in Ózd. The average lead isotopic ratio in soil samples ranged from 1.146 to 1.240 (²⁰⁶Pb/²⁰⁷Pb) for Salgótarján and from 1.084 to 1.240 for Ózd. Total Pb concentration and isotopic ratios of slag and coal samples depicted notable differences as isotopic ratios for Salgótarján and Ózd coals are ²⁰⁶Pb/²⁰⁷Pb:1.175 and ²⁰⁶Pb/²⁰⁷Pb:1.256, respectively. Meanwhile, the lead content in the Salgótarján fly-ash slag (from the coal-fired power plant) was identified as 14 ppm (²⁰⁶Pb/²⁰⁷Pb:1.175, similar to coal). However, the Ózd smelter slag was characterized by high lead concentration (202 ppm) and lowest isotopic composition (²⁰⁶Pb/²⁰⁷Pb=1.118).

To calculate the relative contribution of anthropogenic sources, suggested binary mixing models were used. It is revealed that in Salgótarján soils average 34 % of Pb enters from industrial sources, 43 % from coal, and 23 % from the natural environment. In contrast, in Ózd, the proportion of anthropogenic lead is estimated on average by 53 % from industries (slag), 38 % from coal, and only 9% from natural input. The proportion of coal and slag in the soil samples was proved by thorough microscopy observations and SEM analysis as well.

In conclusion, based on the comprehensive analysis, local smelter and steel-iron industries were the dominant Pb contamination sources in both cities.

 

Keywords: Lead pollution, isotopic ratio, source identification, binary mixing model