A Thirty-Year Record of PTE Pollution in Mangrove Sediments: Implications for Human Activities in Two Major Chinese Metropolises, Shenzhen and Hong Kong

•PTEs (Cr, Ni, Cu, Zn and Pb) were analyzed in sediment cores from four mangroves in Shenzhen and Hong Kong.•Due to different environmental policy and industrial structure, the study areas were in different stages of the environmental Kuznets Curve. Sediment cores from four mangroves in two Chinese metropolises, Shenzhen and Hong Kong, were studied to determine historic trends in regional pollution with potentially toxic elements (PTEs). Physicochemical properties, Cr, Ni, Cu, Zn and Pb contents, and their enrichment factors were determined. Correlation analyses and principle component analyses were conducted to investigate natural influences on PTE distribution, while comparisons between PTE trends and industrial activities in the individual regions were conducted to understand anthropogenic influences over the last thirty years in Shenzhen and Hong Kong. Results indicate that grain size composition and organic matter are the main natural factors affecting PTE distribution laterally and vertically. The relationship between PTE pollution and economic development supports the environmental Kuznets curve (EKC) hypothesis. For example, higher PTE levels in developed regions such as the mangroves of Fu Tian and Mai Po are consistent with an early stage of the EKC, where the environment deteriorates due to increased industrial activity. However, sites where PTE levels have decreased in recent years reflect later stages of the EKC, where environmental quality has improved despite continued economic growth. These insights should allow the development of better policies and regulations for environmental protection and sustainable development of coastal cities.