Mangroves have high ecological service value and play an important role in achieving carbon neutrality. However, the ecological services provided by mangroves are gradually declining due to the threat of various pollutants, especially heavy metal (HM) pollution. Researching the status and history of heavy metals (HMs) in mangrove sediments improves understanding of how mangroves can be protected. We studied the Zhanjiang Bay mangroves, which is an important part of the Zhanjiang Mangrove National Nature Reserve, and is greatly affected by human activities, as an example. We analyzed the pollution levels and deposition process of HMs and their influencing factors. In the mangrove surface sediments of Zhanjiang Bay, Pb, Cr, and Co were slightly to moderate enriched and Cu was moderate-heavy enriched. Zn and Hg showed moderate-heavy enrichment and heavy enrichment, respectively. Cu, Zn, Hg, and Co were 1.5, 1.88, 2.66, and 1.27 times the local background, respectively. Cu, Zn, and Hg mainly originated from anthropogenic sources, and Co may have derived from natural sources. The HM data of mangrove sedimentary cores in Zhanjiang Bay were obtained for the first time; high HM content appeared in the deep layer of the cores but not in the mangrove surface sediments. Both cores were well documented for the effects of natural and anthropogenic factors on the deposition process of HMs. Among them, the high enrichment of Hg in 1909–1921 may be closely related to human activities rather than natural formation. Before 1954, dense mangroves favored the accumulation and gradual increase of HMs. The intense human activity in 1945–1963 during the period of economic construction and reclamation of the Nansan Island Engineering led to significant increases in Cu, Zn, Pb, Cr, and Co, which reached their highest values in more than one hundred years. After 1963, anthropic factors such as deforestation and conversion to aquaculture sharply reduced mangrove area. Reclamation engineering enhanced tidal erosion. Natural factors such as precipitation, storm surge, sea-level rise, and high tides have accelerated the erosion and dilution of mangrove sediments in Zhanjiang Bay. These factors have led to the gradual reduction of HM content in sedimentary cores.

This study aims to characterize heavy metal contamination in rice fields of the Nandu River Basin (subtropical red soil zone) and elucidate its risk mechanisms. Key objectives include assessing pollution levels/ecological risks, identifying contamination sources, and evaluating human health risks from soil-rice systems. Forty paired soil-rice samples were collected. Concentrations of Cr, Ni, Cu, Zn, Pb, Cd, Hg, and As were quantified using ICP-MS and ICP-AES. Contamination status was evaluated via the Nemerow integrated pollution index and Hakanson’s potential ecological risk index. Health risks were assessed using an exposure model. Source apportionment employed a multivariate framework combining correlation analysis, principal component analysis (PCA), and the absolute principal component score–multiple linear regression (APCS-MLR) receptor model. Soil metals generally met screening thresholds, but Hg was significantly enriched (6.44× background), indicating heavy pollution and high ecological risk. Cr exceeded limits in 12% of rice samples; As carcinogenic risk neared thresholds. Hg and Pb in rice showed high spatial variability (CV > 140%), suggesting anthropogenic influence. Source analysis revealed: PC1 (47.3%)—volcanic weathering + traffic/agriculture (Pb-Zn-Ni); PC2 (25.66%)—geogenic + agricultural (As-Cu-Cr); PC3 (10.86%)—electronics/traffic (Hg); PC4 (7.32%)—fertilizers (Cd). Children’s oral intake risk for As/Cr was 78–123% higher than adults; dermal Cr exposure posed notable noncarcinogenic risk ( HQ = 0.709). Contamination in the basin stems from composite natural-anthropogenic sources, with Hg posing significant ecological risk and Cr/As presenting key health concerns, especially for children via ingestion and dermal pathways. These findings provide a scientific basis for targeted risk management of heavy metals in high-background red soil agricultural regions.