Use of lead isotope ratios to assess sources of lead (Pb) dispersed in the urban environments during former industrial activity in the cities of Salgotarjan and Ozd (Hungary)

Lead pollution is a global problem, known to be neurotoxic, especially to children because of its incompatibility and ability to replace essential elements in the body.  However, lead in the environment is derived from multiple (natural and anthropogenic) sources over long time periods. Anthropogenic Pb pollution mainly originates from mining, smelting, industrial uses, waste incineration, coal and leaded gasoline combustion. 

Identification of contamination and source apportionment of lead within the surface urban environment is a challenging task mostly because of coexistence of multiple factors contributing to the elevated concentrations.   Lead has four natural stable isotopes (²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb, and ²⁰⁸Pb) and due to the small fractional mass differences among these isotopes, ordinary chemical, physical or biological reactions cannot obviously influence the isotopic composition of Pb [1]. Thus, it is possible to use stable Pb isotopic composition and/or ratio to trace its sources and transports in the environment. The main aim of this study is to determine the ratios of lead isotopes in urban soil samples to assess contamination sources and finding their connections in two former industrial cites Salgótarján and Ózd, Hungary.

Urban soil samples were collected from residential areas (houses, parks, playgrounds and kindergartens) of Salgótarján and Ózd cities (36 and 60 samples, respectively) where both exposed to the harmful effects of industrial pollutants.  The cities are situated in the same geological formation (e.g. brown coal deposit) and the distance between them is around 40 kilometers and both cities experienced similar industrial history.

Results showed that the average stable lead isotopic ratio of analyzed soil samples is ²⁰⁶Pb/²⁰⁷Pb:1.19 vs ²⁰⁸Pb/²⁰⁷Pb: 2.47 for Salgótarján and ²⁰⁶Pb/²⁰⁷Pb:1.19 vs ²⁰⁸Pb/²⁰⁷Pb: 2.40 for Ózd. In both cities, high significant correlation noted in ²⁰⁶Pb/²⁰⁴Pb vs ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb vs ²⁰⁸Pb/²⁰⁴Pb ratios (R²=0.7 and R²=0.8) reflecting the enrichment of Pb from anthropogenic sources. As the endmembers, stable isotopic ratio of local coal, slag and central European leaded gasoline (²⁰⁶Pb/²⁰⁷Pb:1.11 and ²⁰⁸Pb/²⁰⁷Pb: 2.37) were used. Surprisingly, the stable isotopic ratio depicted considerable difference for coal (²⁰⁶Pb/²⁰⁷Pb: 1.18 vs ²⁰⁸Pb/²⁰⁷Pb: 2.47 and ²⁰⁶Pb/²⁰⁷Pb:1.26 vs ²⁰⁸Pb/²⁰⁷Pb: 2.46) and slag (²⁰⁶Pb/²⁰⁷Pb: 1.18 vs ²⁰⁸Pb/²⁰⁷Pb: 2.46 and ²⁰⁶Pb/²⁰⁷Pb:1.16 vs ²⁰⁸Pb/²⁰⁷Pb: 2.41) from Salgótarján and Ózd. A particular anomaly in Salgótarján was observed for ²⁰⁶Pb/²⁰⁴Pb ratio around the coal-fired power plant where local coal was used as an energy source that might be a part of the explanation for the high ratio. Based on the comprehensive isotopic analysis, data suggested that coal combustion emissions and steelworks were the predominant Pb source in both cities, whereas, vehicular emissions and additional sources (e.g. leaded paint) are no exception.

 

Reference:

[1]         M. Komárek, V. Ettler, V. Chrastný, and M. Mihaljevič, “Lead isotopes in environmental sciences: A review,” Environ. Int., vol. 34, no. 4, pp. 562–577, 2008.