Xuyin Yuan

Characteristics of heavy metal transfer and their influencing factors in different soil-crop systems of the industrialization region, China.

Soil heavy metals and their bioaccumulation in agricultural products have attracted widespread concerns, yet the transfer and accumulation characteristics of heavy metals in different soil-crop systems was rarely investigated. Soil and crop samples were collected from the typical agricultural areas in the Yangtze River Delta region, China. The concentrations of Cu, Pb, Zn, Cd and Hg in the soils, roots and grains of rice (Oryza Sativa L.), wheat (Triticum L.) and canola (Brassica napus L.) were determined in this study. Transfer ability of heavy metals in soil-rice system was stronger than those in soil-wheat and soil-canola systems. The wheat showed a strong capacity to transfer Zn, Cu and Cd from root to the grain while canola presented a restricting effect to the intake of Cu and Cd. Soil pH and total organic matter were major factors influencing metal transfer from soil to rice, whereas soil Al2O3 contents presented a negative effect on heavy metal mobility in wheat and canola cultivation systems. The concentration of Zn and Cd in crop grains could well predicted according to the stepwise multiple linear regression models, which could help to quantitatively evaluate the ecologic risk of heavy metal accumulation in crops in the study area.

SEASONAL VARIATION IN THE MINERALOGY OF THE SUSPENDED PARTICULATE MATTER OF THE LOWER CHANGJIANG RIVER AT NANJING, CHINA

The source and temporal changesof mineralstransported by the world’slarge riversare important. In particular, clay minerals are important in evaluating the maturity of suspended sediments, weathering intensity, and source area. To examine seasonal changes in mineralogical compositions of the Changjiang River (CR), suspended particulate matter (SPM) samples were collected monthly for two hydrological cycles in Nanjing city and then were studied using X-ray diffraction (XRD), diffuse reflectance spectrophotometry (DRS), X-ray fluorescence spectrometry (XRF), and chemical analyses. The resultsindicate that the concentration of CR SPM rangesfrom 11.3 to 152 mg/L and ishighly correlated to the rate of water discharge, with a greater concentration in flood season and lower concentrations during the dry season. CaO, MgO, and Na2O increase with increasing discharge whereas Al2O3 decreases sharply with increasing discharge. Dolomite, calcite, and plagioclase show strikingly similar seasonal variations and increase with increasing discharge with maximum concentrations in the flood season. In contrast, the clay mineral content exhibits the opposite trend with the lowest concentrationsin the flood season. Illite dominatesthe clay mineralsof the CR SPM, followed by chlorite, kaolinite, and smectite. Illite and kaolinite show distinctly seasonal variations; SPM contains more illite and less kaolinite during the flood season than during the dry season. The illite chemistry index and crystallinity, as well as kaolinite/illite ratio, all indicate intense physical erosion in the CR basin during the rainy season. Total iron (FeT) and highly reactive iron (FeHR) concentrations display slight seasonal changes with the smallest values observed during the flood season. Goethite is the dominant Fe oxide mineral phase in the CR SPM and hematite is a minor component, as revealed by DRS analyses. The FeT flux and FeHR flux are 2.786×106 T/y and 1.196×106 T/y, respectively.

Incorporating Bioaccessibility into Human Health Risk Assessment of Heavy Metals in Rice (Oryza sativa L.): A Probabilistic-Based Analysis

A systematic investigation into total and bioaccessible heavy metal concentrations in rice grains harvested from heavy metal-contaminated regions was carried out to assess the potential health risk to local residents. Arsenic, Cr, Cu, Pb, and Zn concentrations were within acceptable levels while Cd and Ni concentrations appeared to be much higher than in other studies. The bioaccessibity of As, Cd, and Ni was high (>25%) and could be well predicted from their total concentrations. The noncarcinogenic risk posed by As and Cd was significant. The carcinogenic risk posed by all bioaccessible heavy metals at the fifth percentile was 10-fold higher than the acceptable level, and Cd and Ni were the major contributors. The contribution of each metal to the combined carcinogenic risk indicates that taking pertinent precautions for different types of cancer, aimed at individuals with different levels of exposure to heavy metals, will greatly reduce morbidity and mortality rates.

Multivariate linear regression model for source apportionment and health risk assessment of heavy metals from different environmental media

The study evaluated source apportionment of heavy metals in vegetable samples from the potential sources of fertilizer, water and soil samples collected along the Changjiang River delta in China. The results showed that 25.72% of vegetable samples (Brassica chinensis L.) containing Pb, and Cd, Cu, Hg and Zn at relatively serious levels were from soil. Combined with principle component analysis (PCA) and cluster analysis (CA), the results of the spatial distribution of heavy metals in different environmental media indicated that fertilizer, water and soil were the main sources of heavy metals in vegetables. The results of multivariate linear regression (MLR) using partition indexes (P) showed that fertilizer contributed to 38.5%, 40.56%, 46.01%, 53.34% and 65.25% of As, Cd, Cu, Pb and Zn contents in vegetables, respectively. In contrast, 44.58% of As, 32.57% of Hg and 32.83% of Pb in vegetables came from soil and 42.78% of Cd and 66.97% of Hg contents in vegetables came from the irrigation water. The results of PCA and CA verified that MLR using P was suitable for determining source apportionment in a vegetable. A health risk assessment was performed; As, Cd and Pb contributed to more than 75% of the total hazard quotient (THQ) values and total carcinogenic risk values (Risktotal) for adults and children through oral ingestion. More than 70% of the estimated THQ and Risktotal is contributed by water and fertilizer. Therefore, it is necessary to increase efforts in screening limits/levels of heavy metals in fertilizer and irrigation water and prioritize appropriate pollution management strategies.