Hefa Cheng

The Challenges and Solutions for Cadmium-contaminated Rice in China: A Critical Review

The wide occurrence of Cd-contaminated rice in southern China poses significant public health risk and deserves immediate action, which arises primarily from extensive metal (including Cd) contamination of paddies with the fast expansion of nonferrous metal mining and smelting activities. Accumulation of Cd in rice grains can be reduced by removing Cd from the contaminated paddy soils, reducing its bioavailability, and controlling its uptake by rice plants. Although a range of measures can be taken to rehabilitate Cd-contaminated lands, including soil replacement and turnover, chemical washing, and phytoremediation, they are either too expensive and/or too slow. Various amendment materials, including lime, animal manures, and biochar, can be used to immobilize Cd in soils, but such fixation approach can only temporarily reduce Cd availability to rice uptake. Cultivation of alternative crops with low Cd accumulation in edible plant parts is impractical on large scales due to extensive contamination and food security concerns in southern China. Transgenic techniques can help develop rice cultivars with low Cd accumulation in grains, but little public acceptance is expected for such products. As an alternative, selection and development of low-Cd rice varieties and hybrids through plant biotechnology and breeding, particularly, by integration of marker-assisted selection (MAS) with traditional breeding, could be a practical and acceptable option that would allow continued rice production in soils with high bioavailability of Cd. Plant biotechnology and breeding can also help develop Cd-hyperaccumulating rice varieties, which can greatly facilitate phytoremediation of contaminated paddies. To eliminate the long-term risk of Cd entering the food chain, soils contaminated by Cd should be cleaned up when cost-effective remediation measures are available.

A method for apportionment of natural and anthropogenic contributions to heavy metal loadings in the surface soils across large-scale regions

Quantification of the contributions from anthropogenic sources to soil heavy metal loadings on regional scales is challenging because of the heterogeneity of soil parent materials and high variability of anthropogenic inputs, especially for the species that are primarily of lithogenic origin. To this end, we developed a novel method for apportioning the contributions of natural and anthropogenic sources by combining sequential extraction and stochastic modeling, and applied it to investigate the heavy metal pollution in the surface soils of the Pearl River Delta (PRD) in southern China. On the average, 45-86% of Zn, Cu, Pb, and Cd were present in the acid soluble, reducible, and oxidizable fractions of the surface soils, while only 12-24% of Ni, Cr, and As were partitioned in these fractions. The anthropogenic contributions to the heavy metals in the non-residual fractions, even the ones dominated by natural sources, could be identified and quantified by conditional inference trees. Combination of sequential extraction, Kriging interpolation, and stochastic modeling reveals that approximately 10, 39, 6.2, 28, 7.1, 15, and 46% of the As, Cd, Cr, Cu, Ni, Pb, and Zn, respectively, in the surface soils of the PRD were contributed by anthropogenic sources. These results were in general agreements with those obtained through subtraction of regional soil metal background from total loadings, and the soil metal inputs through atmospheric deposition as well. In the non-residual fractions of the surface soils, the anthropogenic contributions to As, Cd, Cr, Cu, Ni, Pb, and Zn, were 48, 42, 50, 51, 49, 24, and 70%, respectively.

Exposure and size distribution of nitrated and oxygenated polycyclic aromatic hydrocarbons among the population using different household fuels.

Polycyclic aromatic hydrocarbons (PAHs) derivatives like nitrated and oxygenated PAHs are of growing concerns because of considerably higher toxicity and important roles during atmospheric chemical reactions. Residential solid fuel combustion is likely to be one large primary source of these pollutants in developing countries. In this study, inhalation exposure to nitrated and oxygenated PAH derivatives was evaluated among rural residents using carried samplers. The exposure levels of individual nitrated PAHs ranged from 4.04 (9-nitrated phenanthrene) to 89.8 (9-nitrated anthracene) pg/m(3), and of oxy-PAHs were 0.570 (benzo[a]anthracene-7, 12-dione) to 7.99 (Benzanthrone) ng/m(3), generally higher in wood user than that in anthracite user. A majority of derivatives in particle presented in PM2.5 (80% for nitrated naphthalene and over 90% for other targets) and even fine PM1.0. Mass fractions of PAH derivatives in fine and ultra-fine particles were significantly higher than the fractions of corresponding parent PAHs, indicating more adverse health outcomes induced by these derivatives. The inhalation exposure levels for residents adopting wood gasifier burners was significantly lower than the documented results for those burning wood in typical built-in brick stoves, and comparable to those using LPG and electricity, which provided vital information for clean stove development and intervention programs.

Properties and cellular effects of particulate matter from direct emissions and ambient sources

ABSTRACT The pollution of particulate matter (PM) is of great concern in China and many other developing countries. It is generally recognized that the toxicity of PM is source and property dependent. However, the relationship between PM properties and toxicity is still not well understood. In this study, PM samples from direct emissions of wood, straw, coal, diesel combustion, cigarette smoking and ambient air were collected and characterized for their physicochemical properties. Their expression of intracellular reactive oxygen species (ROS) and levels of inflammatory cytokines (i.e., tumor necrosis factor-α (TNF-α)) was measured using a RAW264.7 cell model. Our results demonstrated that the properties of the samples from different origins exhibited remarkable differences. Significant increases in ROS were observed when the cells were exposed to PMs from biomass origins, including wood, straw and cigarettes, while increases in TNF-α were found for all the samples, particularly those from ambient air. The most important factor associated with ROS generation was the presence of water-soluble organic carbon, which was extremely abundant in the samples that directly resulted from biomass combustion. Metals, endotoxins and PM size were the most important properties associated with increases in TNF-α expression levels. The association of the origins of PM particles and physicochemical properties with cytotoxic properties is illustrated using a cluster analysis.

Public health risk of trace metals in fresh chicken meat products on the food markets of a major production region in southern China

Because most chickens are reared in intensive farms, where a range of feed additives are used routinely, concerns have been raised on the potential public health risk of chicken product consumption. This study was conducted to characterize the contents of trace metals in fresh chicken tissues (354 samples) on the food markets in Guangdong province of southern China, a major region of chicken production with heavy per capita chicken consumption, and to assess the public health risk from chronic dietary exposure to the trace metals through chicken consumption. With the exception of Cr, Ni, and Pb, the contents of trace metals were generally higher in the chicken giblets (livers, gizzards, hearts, and kidneys) compared to muscles (breasts and drumsticks). Chicken tissues from the urban markets generally contained higher levels of As, Cu, Mn, and Zn than those from the rural markets, while the contents of Pb were typically higher in the chicken muscles from the rural markets. Results of statistical analyses indicate that Cu, Zn, and As in the chicken tissues derived mainly from the feeds, which is consistent with the widespread use of Cu, Zn, and phenylarsenic compounds as feed supplements/additives in intensive poultry farming. No non-carcinogenic risk is found with the consumption of fresh chicken meat products on the food markets, while approximately 70% of the adult population in Guangzhou and 30% of those in Lianzhou have bladder and lung cancer risk above the serious or priority level (10-4), which arises from the inorganic arsenic contained in the chicken tissues. These findings indicate that the occurrence of inorganic arsenic at elevated levels in chicken tissues on the food markets in Guangdong province poses a significant public health risk, thus the use of phenylarsenic feed additives in Chinas poultry farming should be significantly reduced and eventually phased out.

Stack and fugitive emissions of major air pollutants from typical brick kilns in China

Little information exists on emission factors (EFs, quantities of pollutants emitted per unit of fuel consumed) for brick kilns in China, although brick kilns are important emission sources of many air pollutants, and 45% of the worlds bricks are produced in China. In this study, EFs of carbon dioxide (CO2), carbon monoxide (CO), sulfur dioxide (SO2), nitrogen oxides (NOx), particulate matters (PMs), black carbon (BC), organic carbon (OC), and polycyclic aromatic hydrocarbons (PAHs) for brick kilns were derived based on field measurements of a total of 18 brick kilns of major types in China. This was the first study to quantify EFs of both stack and fugitive sources based on a modified carbon balance method that was developed for this study. The EFs of most pollutants, especially the incomplete combustion products in fugitive emissions, were much higher than those for stack emissions, indicating a substantial underestimation of total emissions when leakage is not taken into consideration. This novel method can be applied to quantify emissions from other similar sources with both stack and fugitive emissions.

Estimating household air pollution exposures and health impacts from space heating in rural China

Exposure to and the related burden of diseases caused by pollution from solid fuel cooking, known as household air pollution (HAP), has been incorporated in the assessment of the Global Burden of Diseases (GBD) project. In contrast, HAP from space heating using solid fuels, prevalent in countries at middle or high altitudes, is less studied and missing from the GBD assessment. China is an ideal example to estimate the bias of exposure and burden of diseases assessment when space heating is neglected, considering its remarkably changing demands for heating from the north to the south and a large solid-fuel-dependent rural population. In this study, based on a meta-analysis of 27 field measurement studies in rural China, we derive the indoor PM2.5 (fine particulate matter with an aerodynamic diameter smaller than 2.5 μm) concentration for both the heating and non-heating seasons. Combining this dataset with time-activity patterns and percentage of households using solid fuels, we assess the population-weighted annual mean exposure to PM2.5 (PWE) and the health impacts associated with HAP in mainland rural China by county for the year 2010. We find that ignoring heating impacts leads to an underestimation in PWE estimates by 38 μg/m3 for the nationwide rural population (16 to 40 as interquartile range) with substantial negative bias in northern provinces. Correspondingly, premature deaths and disability-adjusted life years will be underestimated by approximately 30 × 103 and 60 × 104 in 2010, respectively. Our study poses the need for incorporating heating effects into HAP risk assessments in China as well as globally.

A novel enhanced diffusion sampler for collecting gaseous pollutants without air agitation

ABSTRACT A novel enhanced diffusion sampler for collecting gaseous phase polycyclic aromatic hydrocarbons (PAHs) without air agitation is proposed. The diffusion of target compounds into a sampling chamber is facilitated by continuously purging through a closed-loop flow to create a large concentration difference between the ambient air and the air in the sampling chamber. A glass-fiber filter-based prototype was developed. It was demonstrated that the device could collect gaseous PAHs at a much higher rate (1.6 ± 1.4 L/min) than regular passive samplers, while the ambient air is not agitated. The prototype was also tested in both the laboratory and field for characterizing the concentration gradients over a short distance from the soil surface. The sampler has potential to be applied in other similar situations to characterize the concentration profiles of other chemicals.

Distinguishing Emission-Associated Ambient Air PM2.5 Concentrations and Meteorological Factor-Induced Fluctuations

Although PM2.5 (particulate matter with aerodynamic diameters less than 2.5 μm) in the air originates from emissions, its concentrations are often affected by confounding meteorological effects. Therefore, direct comparisons of PM2.5 concentrations made across two periods, which are commonly used by environmental protection administrations to measure the effectiveness of mitigation efforts, can be misleading. Here, we developed a two-step method to distinguish the significance of emissions and meteorological factors and assess the effectiveness of emission mitigation efforts. We modeled ambient PM2.5 concentrations from 1980 to 2014 based on three conditional scenarios: realistic conditions, fixed emissions, and fixed meteorology. The differences found between the model outputs were analyzed to quantify the relative contributions of emissions and meteorological factors. Emission-related gridded PM2.5 concentrations excluding the meteorological effects were predicted using multivariate regression models, whereas meteorological confounding effects on PM2.5 fluctuations were characterized by probabilistic functions. When the regression models and probabilistic functions were combined, fluctuations in the PM2.5 concentrations induced by emissions and meteorological factors were quantified for all model grid cells and regions. The method was then applied to assess the historical and future trends of PM2.5 concentrations and potential fluctuations on global, national, and city scales. The proposed method may thus be used to assess the effectiveness of mitigation actions.