Pollution characteristics and sources of soil heavy metals in the carbonate rock region of central Shandong

JIANG Bing; SUN Zengbing; ZHANG Deming; WANG Jian; LIU Yang

doi:10.11932/karst20250410

Abstract：Soil heavy metals in carbonate rock regions often exhibit natural high-background characteristics due to secondary enrichment during pedogenesis,posing potential risks to soil health,agricultural product safety,and ecological sustainability.Understanding the pollution patterns and sources of heavy metals in such high-background zones is critical for formulating targeted environmental protection strategies and safeguarding human health.This study focused on the carbonate rock region of central Shandong,a typical northern Chinese karst region dominated by Cambrian-Ordovician limestone and dolomite as parent rocks.A comprehensive investigation was conducted by collecting and analyzing samples of rock,surface soil,vertical soil profile,and atmospheric dustfall.Multiple analytical methods,including Enrichment Factor(EF)analysis,Principal Component Analysis(PCA),annual heavy metal increment simulation from dustfall,and Pearson correlation analysis,were employed to explore the pollution characteristics,sources,and influencing factors of soil heavy metals. Carbonate rock regions are globally significant for their unique pedogenic processes,where heavy metals undergo secondary enrichment due to intense chemical weathering and leaching of carbonate minerals.This natural enrichment,combined with potential anthropogenic inputs(e.g.,atmospheric dustfall),complicates the identification of heavy metal sources and their ecological impacts.Previous studies have primarily focused on single-medium(soil-only or rock-soil)analyses,lacking systematic multi-medium investigations.This study aimed to bridge this gap by integrating data on rock,soil,and atmospheric dustfall to comprehensively characterize the behavior of heavy metals in carbonate rock regions. The study area,located at the junction of the mountainous area in central Shandong and the northern Shandong plain,experiences a semi-humid continental monsoon climate characterized by distinct seasonal precipitation.Parent rocks are primarily carbonate(limestone and dolomite),with soil development dominated by chemical weathering.Soil samples were collected from natural woodlands and wilderness grasslands with minimal human disturbance.Rock samples were collected at the outcrop of bedrock.Atmospheric dustfall samples were collected over a one-year period of dry deposition.All samples were processed and analyzed in a certified laboratory,with heavy metal concentrations measured by Inductively Coupled Plasma Mass Spectrometry(ICP-MS),X-ray Fluorescence(XRF),and Atomic Fluorescence Spectrometry(AFS).Additionally,physicochemical properties,including pH,cation exchange capacity,and organic matter,were determined. The results show as follows:(1)The contents of soil heavy metals(Cu,Pb,Zn,Cr,Ni,As,Cd,and Hg)are 2.76 to 6.82 times higher than those in parent rocks.The contents of As,Cr,and Ni in atmospheric dustfall is lower than those in soil(enrichment coefficient between 0.47 and 0.65),while the contents of Cu,Pb,Zn,Hg,and Cd are higher(enrichment coefficient between 1.17 and 8.67),with Cd being the most significantly enriched.(2)The average pollution degree of soil heavy metals,ranked by EF values,is:Hg＞Cd＞Ni＞Cu＞As＞Zn＞Pb＞Cr.Most metals exhibit low pollution levels(EF＜2),except for minor Hg cases(EF＞5).Cr and Ni show negligible anthropogenic influence(all EF＜2),while Cd and Hg have relatively higher EF values,indicating potential external inputs.(3)Atmospheric dustfall contribute to the accumulation of soil heavy metals,with annual growth rates calculated as follows:Cd(0.55％),Hg(0.20％),Zn(0.16％),and Pb(0.09％).Cd and Hg,with the highest growth rates,were more significantly affected by dust deposition.(4)Soil Organic Matter(SOM)is strongly correlated with Cd and Hg(P＜0.01),showing similar vertical distribution patterns(surface accumulation).Cation Exchange Capacity(CEC)is significantly correlated with Cu,Pb,Zn,Cr,Ni,and As(P＜0.01),with stable vertical variations.These results indicate that Cd and Hg are primarily controlled by SOM and superimposed by dustfall inputs,while Cu,Pb,Zn,Cr,Ni,and As are mainly derived from parent rock weathering. This study provides a systematic multi-media(rock-soil-dustfall)analysis of heavy metal behavior in carbonate rock regions,emphasizing the combined effects of natural parent materials and anthropogenic dustfall.By integrating enrichment factor analysis,PCA,dustfall increment simulation,and correlation analysis,we identified the sources and controlling factors of soil heavy metals.These findings provide scientific support for strategies of evidence-based soil pollution control in similar carbonate rock regions,particularly prioritizing the management of Cd and Hg based on their higher accumulation rates and anthropogenic contributions.