Prehistoric anthropogenic heavy metal pollution and its correlations with climate evolution on the NE Tibetan Plateau

Metallurgical technology has been a fundamental driver in the evolution of Chinese civilization. Established heavy metal records suggest its introduction into northwestern China occurred around 4000 years ago. However, this timeline is difficult to reconcile with evidence for earlier metallurgical developments documented in other regions of China. This study presents a 12-kyr record of heavy metal pollution and anthropogenic activities, reconstructed from geochemical element concentrations and Pb isotope ratios in the sediments of Hurleg Lake on the northeastern Tibetan Plateau (NE TP). The excess Pb and Cu records reveal the earliest anthropogenic heavy metal pollution occurred at approximately 6.3 cal kyr BP, as supported by a concomitant depletion in ²⁰⁶Pb/²⁰⁷Pb ratios. Furthermore, triple isotope plots identify that the Pb pollution sources in Hurleg Lake sediments were primarily derived from ore mining/metallurgy within the Tibetan Plateau and the Hexi Corridor. Two pronounced periods of heavy metal pollution were identified on the NE TP and Hexi Corridor during 6.3-5.1 cal kyr BP and 4.8-3.4 cal kyr BP, respectively. The first period of intensified pollution on the NE TP coincides with a local warm-wet climate phase. Conversely, the subsequent cold-dry interval (4.8-3.4 cal kyr BP) on the NE TP likely prompted a human migration to the lower-altitude Hexi Corridor, which offered more favorable living conditions. A broader analysis of heavy metal profiles across China identifies five distinct pollution peaks during the Holocene. These findings indicate that metallurgical development in the northwestern region not only predated that of other regions but also potentially predated the previously established timeline of 4000 years. A notable increase in heavy metal concentrations from 4.2 to 2.6 cal kyr BP observed across China was contemporaneous with the archaeologically defined Chinese Bronze Age. This study provides key evidence for the spatiotemporal diffusion of early metallurgical technology within China. It also establishes that sedimentary archives can reliably detect Holocene heavy metal emissions linked to prehistoric and Bronze Age metallurgy.