Hong-Bo Li

Incorporating bioaccessibility into human health risk assessments of heavy metals in urban park soils

Contaminants in urban soils can directly pose significant human health risks through oral ingestion, particle inhalation, and dermal contact, especially for children in public parks. Both non-carcinogenic and carcinogenic risks of heavy metals (Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) were characterized in 40 surface soils (exposed lawns) from 14 urban parks in Xiamen, China. Results based on total metal concentrations may overestimate the actual risks in comparison with oral bioaccessibility assessment that were estimated by a simplified physiologically based extraction test (SBET). After considering the soil-specific bioaccessibility (Cd>Cu>Pb>Mn>Zn>Co~Ni>Cr), the non-cancer hazard of Pb to children via oral ingestion should be a consideration though its Hazard Index (HI) was below one. The overall cancer risks to adults still exceeded the target value 10(-6), mainly contributed by Cr (93.8%) and Pb (6.19%) via dermal contact (68.3%) and oral ingestion (30.4%). To produce a more realistic estimation for human health risks of metal contamination in urban soils, a framework combining land use type and bioaccessibility is recommended and thereby should be applied for the derivation of risk-based, site-specific soil guidelines.

Mechanisms of metal sorption by biochars: Biochar characteristics and modifications

Biochar produced by thermal decomposition of biomass under oxygen-limited conditions has received increasing attention as a cost-effective sorbent to treat metal-contaminated waters. However, there is a lack of information on the roles of different sorption mechanisms for different metals and recent development of biochar modification to enhance metal sorption capacity, which is critical for biochar field application. This review summarizes the characteristics of biochar (e.g., surface area, porosity, pH, surface charge, functional groups, and mineral components) and main mechanisms governing sorption of As, Cr, Cd, Pb, and Hg by biochar. Biochar properties vary considerably with feedstock material and pyrolysis temperature, with high temperature producing biochars with higher surface area, porosity, pH, and mineral contents, but less functional groups. Different mechanisms dominate sorption of As (complexation and electrostatic interactions), Cr (electrostatic interactions, reduction, and complexation), Cd and Pb (complexation, cation exchange, and precipitation), and Hg (complexation and reduction). Besides sorption mechanisms, recent advance in modifying biochar by loading with minerals, reductants, organic functional groups, and nanoparticles, and activation with alkali solution to enhance metal sorption capacity is discussed. Future research needs for field application of biochar include competitive sorption mechanisms of co-existing metals, biochar reuse, and cost reduction of biochar production.

Contamination and source differentiation of Pb in park soils along an urban-rural gradient in Shanghai.

Urban soil Pb contamination is a great human health risk. Lead distribution and source in topsoils from 14 parks in Shanghai, China were investigated along an urban-rural gradient. Topsoils were contaminated averagely with 65 mg Pb kg(-1), 2.5 times higher than local soil background concentrations. HCl-extracts contained more anthropogenic Pb signatures than total sample digests as revealed by the higher (207/206)Pb and (208/206)Pb ratios in extracts (0.8613 ± 0.0094 and 2.1085 ± 0.0121 versus total digests 0.8575 ± 0.0098 and 2.0959 ± 0.0116). This suggests a higher sensitivity of HCl-extraction than total digestion in identifying anthropogenic Pb sources. Coal combustion emission was identified as the major anthropogenic Pb source (averagely 47%) while leaded gasoline emission contributed 12% overall. Urbanization effects were observed by total Pb content and anthropogenic Pb contribution. This study suggests that to reduce Pb contamination, Shanghai might have to change its energy composition to clean energy.

Assessment of in Vitro Lead Bioaccessibility in House Dust and Its Relationship to in Vivo Lead Relative Bioavailability

House dust samples containing 25-738 mg of Pb kg(-1) from 15 cities in China were assessed for in vitro Pb bioaccessibility and in vivo Pb relative bioavailability. On the basis of stable Pb isotope ratios, the Pb in dust samples mainly originated from coal combustion. Lead bioaccessibility was determined using gastric (GP) and intestinal phase (IP) of solubility bioaccessibility research consortium (SBRC), in vitro gastrointestinal (IVG), Deutsches Institut für Normunge.V. (DIN), and physiologically based extraction test methods (PBET), while Pb relative bioavailability (RBA) was determined using a mouse blood model. Lead bioaccessibility in 24 house dust samples varied significantly (23-99%) depending on the methods. Values from the IP were considerably lower than those from the GP because of the co-precipitation of Pb with iron and re-adsorption onto the dust matrix. The SBRC assay with lower GP pH produced higher Pb bioaccessibility because of enhanced Pb dissolution. When compared to mouse blood data using 12 dust samples (29-60%), SBRC-GP and DIN-GP data were correlated with Pb RBA with r(2) values of 0.68 and 0.85 and intercepts 3.15 and 17.4, respectively. Overall, SBRC-GP had potential to predict Pb RBA in dust samples. However, our data suggested that more research is needed to develop a valid in vitro method for predicting Pb RBA in house dust.

Urbanization increased metal levels in lake surface sediment and catchment topsoil of waterscape parks.

Lake surface sediment is mainly derived from topsoil in its catchment. We hypothesized that distribution of anthropogenic metals would be homogenous in lake surface sediment and the lakes catchment topsoil. Anthropogenic metal distributions (cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn)) in fourteen waterscape parks were investigated in surface sediments and catchment topsoils and possible source homogeneity was tested using stable Pb isotopic ratio analysis. The parks were located along an urbanization gradient consisting of suburban (SU), developing urban (DIU), developed urban (DDU), and central urban core (CUC) areas in Shanghai, China. Results indicated that surface lake sediments and catchment topsoils in the CUC parks were highly contaminated by the investigated anthropogenic metals. Total metal contents in surface sediment and topsoil gradually increased along the urbanization gradient from the SU to CUC areas. Generally, the surface sediments had greater total metal contents than their catchment topsoils. These results suggest that urbanization drives the anthropogenic metal enrichment in both surface sediment and its catchment topsoil in the waterscape parks. Soil fine particles (<63 μm) and surface sediments had similar enrichment ratios of metals, suggesting that surface runoff might act as a carrier for metals transporting from catchment to lake. Stable Pb isotope ratio analysis revealed that the major anthropogenic Pb source in surface sediment was coal combustion as in the catchment topsoil. Urbanization also correlated with chemical fractionation of metals in both surface sediment and catchment topsoil. From the SU to the CUC parks, amounts of labile metal fractions increased while the residual fraction of those metals remained rather constant. In short, urbanization in Shanghai drives anthropogenic metal distribution in environmental matrices and the sources were homogenous.

Lead bioaccessibility in 12 contaminated soils from China: Correlation to lead relative bioavailability and lead in different fractions

This study investigated the relationship between Pb relative bioavailability (RBA) and bioaccessibility, and their relationships with Pb in different pools in soils. Twelve Pb-contaminated soils representing different contamination sources from China were analyzed for Pb bioaccessibility using four in vitro methods (UBM, SBRC, IVG, and PBET), Pb-RBA using a mouse blood model, and Pb fractionation using sequential extraction. Lead bioaccessibility in the gastric phase (GP) and Pb-RBA was generally lower in mining soils (0.46-29% and 7.0-26%) than smelting (19-92% and 31-84%) and farming soils (13-99% and 51-61%), with more Pb in the residual fraction in mining soils. Lead bioaccessibility varied with assays, with SBRC (3.0-99%) producing significantly higher bioaccessible Pb than other assays (0.46-84%) in the gastric phase. However, Pb bioaccessibility in the intestinal phase (IP) of all assays sharply decreased to 0.01-20% possibly due to Pb sorption to solid phase at higher pH. Lead bioaccessibility by UBM-GP assay was best correlated with Pb-RBA (r(2) = 0.67), followed by IVG-GP (r(2) = 0.55). Among different Pb fractions, strong correlation was found between Pb bioaccessibility/Pb-RBA and the sum of exchangeable and carbonate fractions. Our study suggested that UBM-GP assay has potential to determine Pb bioaccessibility in contaminated soils in China.

A label-free and portable graphene FET aptasensor for children blood lead detection

Lead is a cumulative toxicant, which can induce severe health issues, especially in children’s case due to their immature nervous system. While realizing large-scale monitoring of children blood lead remains challenging by utilizing traditional methods, it is highly desirable to search for alternative techniques or novel sensing materials. Here we report a label-free and portable aptasensor based on graphene field effect transistor (FET) for effective children blood lead detection. With standard solutions of different Pb2+ concentrations, we obtained a dose-response curve and a detection limitation below 37.5 ng/L, which is three orders lower than the safe blood lead level (100 μg/L). The devices also showed excellent selectivity over other metal cations such as, Na+, K+, Mg2+, and Ca2+, suggesting the capability of working in a complex sample matrix. We further successfully demonstrated the detection of Pb2+ ions in real blood samples from children by using our aptasensors, and explored their potential applications for quantification. Our results underscore such graphene FET aptasensors for future applications on fast detection of heavy metal ions for health monitoring and disease diagnostics.

Bacterial community composition at anodes of microbial fuel cells for paddy soils: the effects of soil properties

PurposeAnode electrogenic bacteria (AEB) widely exist in paddy soils and play an important role in element biogeochemical cycling. However, little information is available on the role of soil characteristics in shaping AEB community. Therefore, the objective of this study was to evaluate the role of soil properties in driving the evolution of anode bacterial communities.Materials and methodsMicrobial fuel cells (MFCs) were constructed for five paddy soils with different chemical properties. The bacterial communities at anodes of closed (MFC running) and open (control) circuit MFCs were characterized using 16S rRNA gene-based Illumina sequencing.Results and discussionPaddy soils with higher dissolved organic carbon (DOC) and ammonium (NH4+) concentrations in porewater showed higher MFC performance. Without MFC running, the dominant bacterial community composition was similar among the used five soils with Clostridia as the dominant bacteria at class level. Compared to control treatments, MFC running significantly decreased bacterial diversity and altered the bacterial community composition at anodes. However, the shift of bacterial communities varied with different types of soils. Betaproteobacteria was enriched by 4–30 times after MFC running for low MFC performance soils, while Deltaproteobacteria enriched (4–20 times) for high MFC performance soils. Redundancy analysis (RDA) indicated that DOC, NH4+, and dissolved ferrous (Fe2+) significantly shift anode bacterial communities for the five soils with MFC running.ConclusionsWe found that high-performing MFCs constructed from paddy soils with high DOC and NH4+ concentrations in porewater selected for an active, highly electrogenic bacterial community (dominated by Deltaproteobacteria) at anodes, while the dominant bacterial community for the low-performing MFCs from soils with low DOC and NH4+ was Betaproteobacteria. These findings imply that soil properties shape the AEB composition, therefore influencing MFC performance. This study provides new insights into the microbial-mediated carbon and nitrogen cycling in paddy soils.

Effect of Lead Pollution Control on Environmental and Childhood Blood Lead Level in Nantong, China: An Interventional Study

Childrens blood lead levels and prevalence of lead poisoning in China are significantly higher than in developed countries, though a substantial decrease has been observed. Since 2011, strict lead control policies in lead-related industries have been implemented in China, but the success of these policies is unknown. In this study, we collected environmental samples, questionnaire data, and blood samples from 106 children from 1 to 14 years old, before and after implementation of lead-usage control policy in wire rope factories by local government in Zhuhang, Nantong in 2012. Results showed that, one year after the lead control, lead concentrations sharply decreased in both environmental and biological samples with a decrease of 0.43 μg/m3 (-84.3%) in ambient air samples, 0.22 mg/kg (-36.1%) in vegetable samples, 441.1 mg/kg (-43.7%) in dust samples, and 6.24 μg/dL (-51.5%) in childhood blood lead levels (BLL). This study demonstrates the success of lead control policies in promoting the prevention and control of childhood lead poisoning in Nantong, China.

Influence of pollution control on lead inhalation bioaccessibility in PM2.5: A case study of 2014 Youth Olympic Games in Nanjing.

Pollution controls were implemented to improve the air quality for the 2014 Youth Olympic Games (YOG) in Nanjing. To investigate the influence of pollution control on Pb inhalation bioaccessibility in PM2.5, samples were collected before, during, and after YOG. The objectives were to identify Pb sources in PM2.5 using stable isotope fingerprinting technique and compare Pb inhalation bioaccessibility in PM2.5 using two simulated lung fluids. While artificial lysosomal fluid (ALF) simulates interstitial fluid at pH 7.4, Gambles solution simulates fluid in alveolar macrophages at pH 4.5. The Pb concentration in PM2.5 samples during YOG (88.2ngm(-3)) was 44-48% lower than that in non-YOG samples. Based on stable Pb isotope ratios, Pb in YOG samples was mainly from coal combustion while Pb in non-YOG samples was from coal combustion and smelting activities. While Pb bioaccessibility in YOG samples was lower than those in non-YOG samples (59-79% vs. 55-87%) by ALF, it was higher than those in non-YOG samples (11-29% vs. 5.3-21%) based on Gambles solution, attributing to the lower pH and organic acids in ALF. Different Pb bioaccessibility in PM2.5 between samples resulted from changes in Pb species due to pollution control. PbSO4 was the main Pb species in PM2.5 from coal combustion, which was less soluble in ALF than PbO from smelting activities, but more soluble in Gambles solution. This study showed it is important to consider Pb bioaccessibility during pollution control as source control not only reduced Pb contamination in PM2.5 but also influenced Pb bioaccessibility.