Philip C. Brookes

Human health risk assessment of heavy metals in soil-vegetable system: a multi-medium analysis.

Vegetable fields near villages in China are suffering increasing heavy metal damages from various pollution sources including agriculture, traffic, mining and Chinese typical local private family-sized industry. 268 vegetable samples which included rape, celery, cabbages, carrots, asparagus lettuces, cowpeas, tomatoes and cayenne pepper and their corresponding soils in three economically developed areas of Zhejiang Province, China were collected, and the concentrations of five heavy metals (Pb, Cd, Cr, Hg and As) in all the samples were determined. The health risk assessment methods developed by the United States Environmental Protection Agency (US EPA) were employed to explore the potential health hazards of heavy metals in soils growing vegetables. Results showed that heavy metal contaminations in investigated vegetables and corresponding soils were significant. Pollution levels varied with metals and vegetable types. The highest mean soil concentrations of heavy metals were 70.36 mg kg(-1) Pb, 47.49 mg kg(-1) Cr, 13.51 mg kg(-1) As, 0.73 mg kg(-1) for Cd and 0.67 mg kg(-1) Hg, respectively, while the metal concentrations in vegetables and corresponding soils were poorly correlated. The health risk assessment results indicated that diet dominated the exposure pathways, so heavy metals in soil samples might cause potential harm through food-chain transfer. The total non-cancer and cancer risk results indicated that the investigated arable fields near industrial and waste mining sites were unsuitable for growing leaf and root vegetables in view of the risk of elevated intakes of heavy metals adversely affecting food safety for local residents. Chromium and Pb were the primary heavy metals posing non-cancer risks while Cd caused the greatest cancer risk. It was concluded that more effective controls should be focused on Cd and Cr to reduce pollution in this study area.

Physicochemical properties of biochar produced from aerobically composted swine manure and its potential use as an environmental amendment

Biochars derived from the pyrolysis, at 400 and 700°C, respectively, of fresh (T0), 21d (T1) and 84d (T2) aerobically composted swine manure, were characterized and investigated for their potential use as environmental amendments. The biochar yield significantly increased following composting, but decreased with increased temperature. The ash content, surface area (SA), pH, electrical conductivity (EC), mineral nutrients, total heavy metals (except Cd) and available As, Cu, Mn and Zn concentrations of biochar produced at 700°C were higher than in biochar produced at 400°C, whereas the volatile matter, higher heating value (HHV) and elemental composition were decreased. The maximum Cu(II) adsorption capacity was 20.11 mg g(-1) by biochar produced from T2 at 400°C. The pyrolysis of 84d aerobically composted swine manure to produce biochar at 400°C could be used as a soil amendment, or as an adsorbent for the removal heavy metal ions from wastewater.

The identification of 'hotspots' of heavy metal pollution in soil-rice systems at a regional scale in eastern China.

Chinese agricultural soils and crops are suffering from increasing damage from heavy metals, which are introduced from various pollution sources including agriculture, traffic, mining and especially the flourishing private metal recycling industry. In this study, 219 pairs of rice grain and corresponding soil samples were collected from Wenling in Zhejiang Province to identify the spatial relationship and pollution hotspots of Cd, Cu, Ni and Zn in the soil-rice system. The mean soil concentrations of heavy metals were 0.316 mg kg(-1) for Cd, 47.3 mg kg(-1) for Cu, 31.7 mg kg(-1) for Ni and 131 mg kg(-1) for Zn, and the metal concentrations in rice grain were 0.132 mg kg(-1) for Cd, 2.46 mg kg(-1) for Cu, 0.223 mg kg(-1) for Ni and 17.4 mg kg(-1) for Zn. The coefficient of variability (CV) of soil Cd, Cu and rice Cd were 147%, 146% and 180%, respectively, indicating an extensive variability. While the CVs of other metals ranged from 23.4% to 84.3% with a moderate variability. Kriging interpolation procedure and the Local Morans I index detected the locations of pollution hotspots of these four metals. Cd and Cu had a very similar spatial pattern, with contamination hotspots located simultaneously in the northwestern part of the study area, and there were obvious hotspots for soil Zn in the north area, while in the northeast for soil Ni. The existence of hotspots may be due to industrialization and other anthropogenic activities. An Enrichment Index (EI) was employed to measure the uptake of heavy metals by rice. The results indicated that the accumulation and availability of heavy metals in the soil-rice system may be influenced by both soil heavy metal concentrations and soil physico-chemical properties. Cross-correlograms quantitatively illustrated that EIs were significantly correlated with soil properties. Soil pH and organic matter were the most important factors controlling the uptake of heavy metals by rice. As results, positive measures should be taken into account to control soil pollution and to curtail metal contamination to the food chain in the areas of Wenling, which were the most polluted by toxic metals.

Enhanced abiotic and biotic contributions to dechlorination of pentachlorophenol during Fe(III) reduction by an iron-reducing bacterium Clostridium beijerinckii Z.

A novel Fe(III) reducing bacterium, Clostridium beijerinckii Z, was isolated from glucose amended paddy slurries, and shown to dechlorinate pentachlorophenol (PCP). Fifty percent of added PCP was removed by C. beijerinckii Z alone, which increased to 83% in the presence of both C. beijerinckii Z and ferrihydrite after 11 days of incubation. Without C. beijerinckii Z, the surface-bound Fe(II) also abiotically dechlorinated more than 40% of the added PCP. This indicated that the biotic dechlorination by C. beijerinckii Z is a dominant process causing PCP transformation through anaerobic dechlorination, and that the dechlorination rates can be accelerated by simultaneous reduction of Fe(III). A biochemical electron transfer coupling process between sorbed Fe(II) produced by C. beijerinckii Z and reductive dehalogenation is a possible mechanism. This finding increases our knowledge of the role of Fe(III) reducing genera of Clostridium in dechlorinating halogenated organic pollutants, such as PCP, in anaerobic paddy soils.

Effects of inorganic and organic amendments on the uptake of lead and trace elements by Brassica chinensis grown in an acidic red soil.

A greenhouse study was conducted to investigate the effects of inorganic (phosphate rock, single superphosphate and calcium magnesium phosphate) and organic amendments (peat, straw manure and pig manure) on the uptake of lead (Pb) and trace elements by Chinese Cabbage (Brassica chinensis) grown in an acidic red soil. The application of all organic amendments increased the soil pH while inorganic amendments such as single superphosphate did not. Both inorganic and organic amendments decreased the availability and uptake of Pb while the organic amendments were superior to the inorganic (phosphate) amendments in reducing the availability of the more labile (soluble and exchangeable Pb) forms of soil Pb. More Pb was taken up by roots than shoots with all soil amendments. Among the organic amendments, straw manure and pig manure caused the largest decrease in Pb availability at 456.5 and 457.3 mg kg(-1), respectively, when a high level of 30 g organic amendments kg(-1) was applied. The organic amendments greatly increased the fraction D targeted to Fe-Mn oxides bound Pb, and decreased the fraction A (water-soluble), B (exchangeable), and C (carbonate-bound), thereby decreasing the solubility and mobility of Pb in soil. The organic amendments also significantly improved the concentrations of Fe, Mn, Cu and Zn in the soil and shoots (except Fe in shoots and/or roots), which are essential for plant nutrition. The organic amendments of straw and pig manure lowered the availability and uptake of Pb but not that of other trace metals. Thus, these amendments have the potential to remediate Pb-contaminated soils in situ.

Potential role of biochars in decreasing soil acidification - A critical review

A large number of soils, worldwide, are acid (normally pH<5.5) and suffering from on-going soil acidification. Acid soils or soils undergoing acidification generally have low fertility and low crop productivity. Biochars have been reported to be of potential value in agriculture for improving soil properties and in reducing the hazards caused by soil acidification and in naturally acidic soils. However, the ameliorant effects of biochars on acid soils and the mechanisms involved have not previously been critically reviewed. Here we summarize the phenomena, and mechanisms involved in the improvement of soil acidity by biochars, the alleviation of aluminum toxicity, the enhancement of nutrient availability, and changes in nitrification by collating data in the literature. In addition, the agronomic effectiveness and environmental concerns in the incorporation of biochar and other soil additives (i.e. lime, industrial by-products, organic wastes and plant residues) to acid soils are systemically compared. We conclude that biochar is a potentially effective amendment to reverse or to prevent acidification in acid soils. Finally, perspectives for further research in terms of soil acidification are presented to address some issues that are still poorly understood and/or highly controversial.

Zeolite-supported nanoscale zero-valent iron: New findings on simultaneous adsorption of Cd(II), Pb(II), and As(III) in aqueous solution and soil

Nanoscale zero-valent iron (NZVI) has a high adsorption capacity for heavy metals, but it forms aggregates easily. In this study, zeolite-supported nanoscale zero-valent iron (Z-NZVI) was synthesized from a simplified liquid-phase reduction of iron(III) salts which simultaneously adsorbed As(III), Cd(II) and Pb(II) from aqueous solution and soil. Scanning electron micrographs showed that aggregation was eliminated and the NZVI evenly dispersed onto the surface of zeolite. FTIR spectra reveal that NZVI was protected from oxidization on the surface of Z-NZVI. XRD and XPS patterns confirmed the formation of Cd(OH)2, Pb0, and FeAsO4 in Z-NZVI after adsorption. The experimental maximum adsorption capacity of Z-NZVI was 11.52mg As(III)/g, 48.63mg Cd(II)/g, and 85.37mg Pb(II)/g at pH 6, respectively, much higher than that of zeolite. Batch experiments indicate that various adsorption mechanisms including electrostatic adsorption, ionic exchange, oxidation, reduction, co-precipitation, and complexation coexisted with the selected heavy metals. Due to the formation of multiphase compounds on the Z-NZVI, the synergy and competition among heavy metals were concurrent. Most arsenic, cadmium and lead in the soil samples were immobilized after mixing with 30g/kg Z-NZVI. These results suggest that Z-NZVI has great potential for treating water and soil multi-contaminated with heavy metals.

Opportunities for Phytoremediation and Bioindication of Arsenic Contaminated Water Using a Submerged Aquatic Plant:Vallisneria natans (lour.) Hara.

The identification of plants with high arsenic hyperaccumulating efficiency from water is required to ensure the successful application of phytoremediation technology. Five dominant submerged plant species (Vallisneria natans (Lour.) Hara., Potamageton crispus L., Myriophyllum spicatum L., Ceratophyllum demersum L. and Hydrilla verticillata (L.f.) Royle) in China were used to determine their potential to remove As from contaminated water. V. natans had the highest accumulation of As among them. The characteristics of As accumulation, transformation and the effect of phosphate on As accumulation in V. natans were then further studied. The growth of V. natans was not inhibited even when the As concentration reached 2.0 mg L−1. After 21 d of As treatment, the bioconcentration factor (BCF) reached 1300. The As concentration in the environment and exposure time are major factors controlling the As concentration in V. natans. After being absorbed, As(V) is efficiently reduced to As(III) in plants. The synthesis of non-enzymic antioxidants may play an important role under As stress and increase As detoxication. In addition, As(V) uptake by V. natans was negatively correlated with phosphate (P) uptake when P was sufficiently supplied. As(V) is probably taken up via P transporters in V. natans.

Interaction between the Microbial Community and Invading Escherichia coli O157:H7 in Soils from Vegetable Fields

ABSTRACT The survival of Escherichia coli O157:H7 in soils can contaminate vegetables, fruits, drinking water, etc. However, data on the impact of E. coli O157:H7 on soil microbial communities are limited. In this study, we monitored the changes in the indigenous microbial community by using the phospholipid fatty acid (PLFA) method to investigate the interaction of the soil microbial community with E. coli O157:H7 in soils. Simple correlation analysis showed that the survival of E. coli O157:H7 in the test soils was negatively correlated with the ratio of Gram-negative (G−) to Gram-positive (G+) bacterial PLFAs (G−/G+ ratio). In particular, levels of 14 PLFAs were negatively correlated with the survival time of E. coli O157:H7. The contents of actinomycetous and fungal PLFAs in the test soils declined significantly (P, <0.05) after 25 days of incubation with E. coli O157:H7. The G−/G+ ratio declined slightly, while the ratio of bacterial to fungal PLFAs (B/F ratio) and the ratio of normal saturated PLFAs to monounsaturated PLFAs (S/M ratio) increased, after E. coli O157:H7 inoculation. Principal component analysis results further indicated that invasion by E. coli O157:H7 had some effects on the soil microbial community. Our data revealed that the toxicity of E. coli O157:H7 presents not only in its pathogenicity but also in its effect on soil microecology. Hence, close attention should be paid to the survival of E. coli O157:H7 and its potential for contaminating soils.

Survival of Escherichia coli O157:H7 in Soils from Jiangsu Province, China

Escherichia coli O157:H7 (E. coli O157:H7) is recognized as a hazardous microorganism in the environment and for public health. The E. coli O157:H7 survival dynamics were investigated in 12 representative soils from Jiangsu Province, where the largest E. coli O157:H7 infection in China occurred. It was observed that E. coli O157:H7 declined rapidly in acidic soils (pH, 4.57 – 5.14) but slowly in neutral soils (pH, 6.51 – 7.39). The survival dynamics were well described by the Weibull model, with the calculated td value (survival time of the culturable E. coli O157:H7 needed to reach the detection limit of 100 CFU g−1) from 4.57 days in an acidic soil (pH, 4.57) to 34.34 days in a neutral soil (pH, 6.77). Stepwise multiple regression analysis indicated that soil pH and soil organic carbon favored E. coli O157:H7 survival, while a high initial ratio of Gram-negative bacteria phospholipid fatty acids (PLFAs) to Gram-positive bacteria PLFAs, and high content of exchangeable potassium inhibited E. coli O157:H7 survival. Principal component analysis clearly showed that the survival profiles in soils with high pH were different from those with low pH.