[Cadmium Enrichment and Bioavailability of Quaternary Profiles in Nansha District, Guangzhou, China].

Comprehending the distribution pattern and enrichment rule of the heavy metal cadmium (Cd) in soil and grasping its activity and influencing factors is crucial for guaranteeing the soil environment safety of agricultural and construction land and improving the overall quality of the soil environment. The concentration of heavy metal Cd in the quaternary profile of Nansha was measured, and the pollution level was evaluated using the geographical accumulation index (Igeo) and potential ecological risk index (Er). Then, we determined the correlation between the total amount of Cd and the physicochemical properties of the soil using factor analysis (FA-MLR). The results showed that the average content of Cd in shallow soil (0-20 cm) in the Nansha area was 0.54 mg·kg-1, and the soil was mainly weakly acidic and neutral. The average content of Cd in deep soil (150-200 cm) was 0.42 mg·kg-1, and the soil was mainly neutral. At the same time, the variation coefficient of Cd content in shallow soil was significantly greater than that in deep soil, and Cd content tended to be consistent with the increase in depth. The Cd content of quaternary sediments showed a bimodal distribution with depth, reaching a peak at 20-25 m and 5-10 m, respectively, whereas the core sediments in this section were mostly marine sediments of silt and silty clay, with high cation exchange capacity and organic matter. The Igeo and Er of Cd in the fine-grained sediments dominated by clayey soil were significantly higher than those in the coarse-grained sediments dominated by sandy soil. The difference in soil pH value led to the different trend of Cd content with depth; the migration amount and vertical migration depth of Cd in deep soil were greater in the acidic environment. The influence of pH change on the migration and transformation of Cd was not completely reflected in the influence on the total amount of Cd, but more importantly, it changed the effective state of Cd, thus affecting the bioavailability of Cd. The unstable Cd composed of water-soluble, ion-exchangeable, and carbonate states accounted for 37.92%-49.10% of the total Cd, resulting in a strong instability of soil Cd. Further investigation on the migration and toxicity of heavy metals associated with human health risks is needed in future studies.

[Bioavailability and Ecological Risk Assessment of Cadmium in the Sea-Land Interaction Sediments of the Pearl River Delta].

Cadmium (Cd) pollution poses a threat to human health, and research on Cd bioavailability as well as its ecological risk assessment can help prevent and mitigate Cd hazards. The enrichment characteristics and variability of Cd were investigated in sea-land interaction soil fractions and the associated environmental and ecological risks were evaluated using the accumulation index (Igeo), potential ecological hazard index (Er), and risk assessment coding (RAC). The results showed that:① The Cd content of miscellaneous fill material was typically lower than 0.3 mg·kg-1 and that of plain full was higher than 0.3 mg·kg-1. The Cd content of marine sediment was significantly higher than that of continental sediments, averaging 0.36 and 0.10 mg·kg-1, respectively. The concentration of Cd in marine sediments buried at shallow depths (<5 m) was generally higher than at greater depths (>5 m). ② There was a moderate correlation between Cd and CEC in artificial fill (Q4ml; correlation coefficient=0.52, P<0.05). There was a weak correlation between Cd and organic matter in the marine sediments (correlation coefficient=0.49, P<0.05). Total cadmium and the physical and chemical properties of soil had a significant influence on the fraction of soil cadmium. ③ The Igeo of artificially fill and marine sediment was dominated by the relationship 1 < Igeo < 2, which indicated a moderate level of pollution. The Er of artificial fill and marine sediment was mainly 80 < Er < 160, indicating a high potential ecological hazard. Soil acid-extractable Cd accounted for more than 50% of the total Cd in each drill hole, which generally indicated a very high potential ecological risk. These results provide a basis for environmental and agricultural decision-making and provide theoretical guidance for soil pollution investigations and remediation.

[Content and Distribution of Cadmium in Soil and Fluvial Sediments in the Sea-Land Interaction Zone].

Cadmium pollution poses a threat to human health. The examination of spatial distribution of Cd in soils can be used to assess the risks posed to humans and the environment. The enrichment characteristics and variation rules of heavy metal cadmium in the soil were revealed by analyzing the concentration and fractions of Cd in the soil at different depths in the sea-land interaction zone. The results showed that: ① the concentration of Cd in the surface water of Nansha was lower than 0.0001 mg ·L-1, and the physical and chemical properties of river sediments showed spatial differences with the boundary of "Shang Heng-li River". Cd was mainly deposited in the north of the "Shang Heng-li River", with the mean total Cd of 2.71 mg ·kg-1. The total Cd in the sediment of the "Shang Heng-li River" and the rivers south of it were 0.062-0.39 mg ·kg-1, which caused minimal harm to the marine environment. ② The content of Cd in the soil profile gradually decreased with an increase in soil burial depth. The median content of Cd in the five layers, including 0-20 cm, 20-50 cm, 50-90 cm, 90-140 cm, and 140-200 cm, were 0.51, 0.50, 0.45, 0.42, and 0.33 mg ·kg-1, respectively, and the dispersion degree gradually decreased with an increase in buried depth; the vertical migration amount and migration depth of Cd increased significantly in soils with pH less than 5. ③ The residual Cd in the soil accounted for approximately 40%, and the trend was typically flat with a change in buried depth. The median proportion of acid soluble Cd was consistent with the change in pH and increased with an increase in the buried depth of the profile, while the median proportion of reducible Cd was consistent with the change in iron and manganese content, and decreased with an increase in buried depth of section. These results have important guiding significance for the regional prevention and control of Cd pollution in farmland surrounding cities and the treatment and remediation of polluted soil.