Predicting the probability distribution of Pb-increased lands in sewage-irrigated region: A case study in Beijing, China

Assessment of pollution risk and spatial distribution for pollutant are important in the research of regional soil environmental quality. The paper provides a case of geostatistical method for predicting the probability of exceeding a Pb threshold and tracing the hotspots in sewage-irrigated land. The hotspots of Pb pollution which indicated higher risk than other areas were identified to be mainly distributed in the regions of soils irrigated with sewage. Sewage irrigation and parent material are the main sources for Pb concentration in soils of the study area, which obviously affect the distribution of Pb. The direction of high spatial continuity is consistent with the main direction of the river (Yongding River). Moreover, the Pb concentrations showed more extended transportation along the main direction of Yongding River. The results of disjunctive kriging showed that, if we are only willing to accept land for vegetable production if the probability that soil lead concentrations exceed the contamination threshold is 50% or more, then 6.2% of the study area (1932 km²) would be classified as unsafe for this purpose. That avoids the difficulty in selecting the proper criterion for the probability threshold.