Using soil properties to predict in vivo bioavailability of lead in soils

A global meta-analysis of the correlation between soil physicochemical properties and lead bioaccessibility

Soil physiochemical properties play a vital role in bioaccessibility-based health risk assessment as it can determine the bioaccessibility and the true risk of potentially toxic elements in soil. However, the effects of soil properties on bioaccessibility still remains unclear. In this paper, 17 of the 1454 literatures with 474 samples were identified, screened and reviewed for exploring the correlation between soil physicochemical properties and lead bioaccessibility (BAc_Pb) through a meta-analysis approach. Five soil physicochemical parameters including pH, SOM, Clay, CEC and T-Pb were systematically analyzed using Principal component analysis, Pearson correlation analysis and survival analysis. The results showed that pH of simulated gastric juice is a major source of heterogeneity of the correlation between soil pH and BAc_Pb. In the gastric phase, the effect of alkaline soil on high BAc_Pb (BAc >50%) is more sensitive, and the effect of acidic soil on low BAc_Pb (BAc <50%) is more sensitive. However, in the small intestinal phase, soil pH displays little impacts on BAc_Pb in acidic, alkaline and neutral soils. Although three principal components explained 66.2% and 64.9% of the total variance of the urban, agricultural, and mining soils in gastric and small intestinal phases, respectively, there was no strong evidence that soil type can influence the BAc_Pb. The results of present study provide insights into the correlation between soil properties and BAc_Pb, and prediction of the bioaccessibility and bioavailability of Pb in different types of soil.

Can the mouse model successfully predict mixed metal(loid)s bioavailability in humans from contaminated soils?

Mouse models have been employed by many scientific research groups worldwide to predict the bioavailability of metal (loid)s and other chemicals in humans. Their suitability for predicting mixed metal (loid) bioavailability has been questioned and debated for decades by many research teams. In this study soils contaminated by lead (Pb) and arsenic (As), either in the field or by spiking in the laboratory, were used in bioavailability and bioaccessibility tests. The spiked soils were aged for more than a year prior to testing to achieve steady state and eliminate soil ageing effects, as reported in previous research. The bioavailability of, firstly, Pb in the presence of As and secondly, As in the presence of Pb was determined using mice. Furthermore, bioaccessibility was determined using a range of in vitro methods: relative bioaccessibility leaching procedure (RBALP), the Unified Bioaccessibility Research Group Europe (BARGE) method (UBM) gastric and intestinal phases, and the National Institute for Public Health and the Environment (RIVM) gastric and intestinal phases. The correlations between Pb and As bioavailability and their in vitro bioaccessibility when they were present in mixtures were analysed. The results indicated that the bioavailability of Pb in mice kidney tissues significantly correlated with bioaccessibility of Pb in RBALP (p < 0.01), UBM gastric (p < 0.01) and intestinal phases (p < 0.01) and RIVM gastric phases when Pb is present in metal (loid) mixtures. Results of the current study reveal that the RBALP, and UBM gastric and intestinal phase were by far the best methods for predicting the RB of Pb when it is present in metal (loid) mixtures. Consequently, the mouse model can successfully explain the in vivo in vitro correlation (IVIVC) of Pb when it is present in metal (loid) mixtures. However, we did find that a mouse model may not be the best one to explain the IVIVC of As when it is present in metal (loid) mixtures.

Phytoremediation of a pyrene-contaminated soil by Cannabis sativa L. at different initial pyrene concentrations

This study proposes the phytoremediation of a pyrene (PYR)-contaminated soil by Cannabis sativa L. The experimental campaign was conducted along a 60 days period using three different initial PYR concentrations (i.e., 50, 100 and 150 mg kg TS^-1 of soil) in 300 mL volume pots under greenhouse conditions (18-25 °C and 45-55% humidity). After 60 days of hemp growth and flourishing, the highest PYR removal reached approximately 95% in planted soil, 35% higher than in the unplanted control. PYR accumulation was observed in both roots and aerial parts of the plant, with a higher PYR uptake at increasing initial PYR concentrations in soil. The initial PYR concentration affected the growth and, thus, the phytoremediation potential of C. sativa L., which was the result of different removal mechanisms. Overall, the lowest initial PYR concentration was the one that resulted in the highest PYR removal. The interaction between the plant roots and microorganisms in rhizosphere was likely associated with PYR removal in this study. The highest DHO activity of 66.26 μg INTF g^-1 TS^-1 was observed in the soil spiked with 50 mg PYR·kg TS^-1.

Gut microbes modulate bioaccessibility of lead in soil

Metabolic uptake of lead (Pb) is controlled by its bioaccessibility. Most studies have examined bioaccessibility of Pb in the absence of gut microbes, which play an important role in the metabolic uptake of nutrients and metal(loid)s in intestine. In this study, we examined the effect of three gut microbes, from various locations in the gut, on the bioaccessibility of soil ingested Pb. The gut microbes include Lactobacillus acidophilus, Lactobacillus rhamnosus and Escherichia coli. Lead toxicity to these three microbes was also examined at various pH values. Bioaccessibility of Pb was measured using gastric and intestinal extractions. Both Pb spiked and Pb-contaminated shooting range field soils were used to measure Pb bioaccessibility in the presence and absence of gut microbes. The results indicated that Pb toxicity to gut microbes, as measured by LD₅₀ value, decreased with increasing pH, and was higher for Lactobacillus species. Gut microbes decreased the bioaccessible Pb; the effect was more pronounced at low pH, mimicking gastric conditions than in conditions closer to the intestine. Lead adsorption by these microbes increased at the higher pH tested, and E. coli adsorbed higher amounts of Pb than did the Lactobacillus species. The effect of gut microbes on reducing Pb bioaccessibility may be attributed to microbially-induced immobilization of Pb through adsorption, precipitation, and complexation reactions. The study demonstrates that bioaccessibility and subsequently bioavailability of metal(loid)s can be modulated by gut microbes, and it is important to undertake bioaccessibility measurements in the presence of gut microbes.

The influence of long-term ageing on arsenic ecotoxicity in soil

The ageing of a contaminant in soil influences the bioavailability and toxicity of environmental pollutants. Yet, despite arsenic (As) being an important terrestrial contaminant, the effect of As ageing on phytotoxicity has received relatively little research. Research to date has reported predominantly short term (< 0.5 years) experiments. Here, we studied the influence of ageing over 0.25 and 5 years on the phytotoxicity of As (as arsenate) on Cucumis sativus L. (cucumber). The study showed that increasing ageing time of As from 0.25 to 5 years increased the EC₁₀ and EC₅₀ values by 4.0 and 1.76 fold, respectively. The dependence of ageing on soil properties was also examined, although only Freundlich sorption parameters were correlated to the ageing factor (r = 0.68, P = 0.028). Soils with high adsorption capacity also showed the greatest change in toxicity over 5 years. In addition, data was compiled from relevant literature to develop a model for As ecotoxicity. The combined model (n = 54) showed no relationship with pH but was correlated to the oxalate extractable iron content and %clay. Arsenate ecotoxicity (EC₅₀, mg/kg) in the multivariate model was related to oxalate iron content, %clay and ageing time. Thus, the results of this study have significant implications for risk assessment of long-term As contaminated soils.

Lead bioaccessibility in farming and mining soils: The influence of soil properties, types and human gut microbiota

To better understand the risk assessment of Lead (Pb) in contaminated soils, 78 soil samples were collected from different locations in China and Pb bioaccessibility was assessed using the PBET (The Physiologically Based Extraction Test) method combined with SHIME (The Simulator of the Human Intestinal Microbial Ecosystem), and Pb bioaccessibility data from the PBET method on 88 soil samples that found in the literature were also used for the assessment. For all the soils, the mean Pb bioaccessibility was as follows: the gastric phase (31.25%) > colon phase (17.78%) > small intestinal phase (10.13%). The values of Pb bioaccessibility in most soils were lower than 60%, which is the typical default assumption for Pb (RBA, relatively bioavailability) by the US EPA. Mean Pb bioaccessibility (41.10% and 14.00% for gastric and small intestinal phases, respectively) in the present study was slightly higher than the values from the literature (24.80% and 8.68% for gastric and small intestinal phases, respectively) in the gastrointestinal tract. Mean Pb bioaccessibility was lower in acidic soil during the small intestinal phase, while the values for the alkaline soil were higher in the small intestinal and colon phases. In the gastric and small intestinal phases, mean Pb bioaccessibility in farming soils was slightly lower than it was in mining soils. However, the mean Pb bioaccessibility from farming soils was increased compared with mining soils in the colon phase given the action of human gut microbiota. Soil pH and type are important factors for predicting soil Pb bioaccessibility and health risk.

Effect of plant-growth-promoting rhizobacteria on phytoremediation efficiency of Scirpus triqueter in pyrene-Ni co-contaminated soils

The aim of this study was to investigate whether the plant-growth-promoting rhizobacteria (PGPR) could enhance phytoremediation efficiency of Scirpus triqueter (S.triqueter) in the pyrene-Ni co-contaminated soil. We also expected to reveal the possible mechanism for the affected phytoremediation efficiency induced by PGPR. We used three kinds of contaminated soils (Ni-contaminated soil, pyrene-contaminated soil and pyrene-Ni co-contaminated soil) to conduct this pot study. After harvest, plants growth indicators, polyphenol oxidase (PPO) activity and soil microbial community structure of each treatment were investigated to explain the different dissipation rates of pyrene and removal rates of Ni between treatments with and without PGPR. The results showed that PGPR-inoculated S. triqueter increased dissipation rates of pyrene and removal rates of Ni in all three contaminated soils, among which Ni removal rates in Ni single contaminated soil was elevated most significantly, from 0.895‰ to 8.8‰, increasing nearly 9 folds. However, Ni removal rate efficiency in co-contaminated soil was weakened because more toxic and complicated co-contaminated soil restrained plant growth and Ni absorption. We also observed that co-contamination harmed the soil microbial community more severely than that in single pyrene or Ni contaminated soil through phospholipid fatty acids analysis. Furthermore, dissipation rates of pyrene and removal rates of Ni were found positively correlated to the PPO activity and the abundance of branched and saturated fatty acids reflected by Pearson correlation analysis.

Lead was mobilized in acid silty clay loam paddy soil with potassium dihydrogen phosphate (KDP) amendment

The immobilization effectiveness between Pb and phosphorus in soil varies with soil types. To clarify the effect of phosphate on the availability of Pb in agricultural soil, a culture experiment with three types of paddy soil was performed with potassium dihydrogen phosphate (KDP) added. EDTA, DGT and in-situ solution extraction methods were used to represent different available Pb content. Results showed that the concentration of EDTA-Pb in HN soil was slightly elevated after exogenous KDP added. The supplement of 300 mg/kg KDP significantly increased the content of soluble Pb in both acid silty clay loam soil and neutral silty loam soil (increased by 104.65% and 65.12%, respectively). However, there was no significant influence of KDP on the concentration of DGT extracted Pb. XANES results showed that Pb(OH)₂, PbHPO₄, humic acid-Pb and GSH-Pb were the major speciation of Pb in soil colloids. The proportion of Pb(OH)₂ and humic acid-bounded Pb in soil colloids were elevated after exogenous KDP added. Our results indicated that there was a mobilization effect of KDP on Pb by increasing the amount of colloidal Pb in soil solution, especially in acid silty clay loam paddy soil. Such colloid-facilitated transport might promote the uptake of Pb in rice and pose a potential threat to human health.

Phytoremediation: Environmentally sustainable way for reclamation of heavy metal polluted soils

Soil contamination with toxic metals is a widespread environmental issue resulting from global industrialization within the past few years. Therefore, decontamination of heavy metal contaminated soils is very important to reduce the associated risks and for maintenance of environmental health and ecological restoration. Conventional techniques for reclamation of such soils are expensive and environmental non-friendly. Phytoremediation is an emerging technology implementing green plants to clean up the environment from contaminants and has been considered as a cost-effective and non-invasive alternative to the conventional remediation approaches. There are different types of phytoremediation including, phytostabilization, phytostimulation, phytotransformation, phytofiltration and phytoextraction, the latter being most extensively acknowledged for remediation of soils contaminated with toxic heavy metals. Recent literature is gathered to critically review the sources, hazardous effects of toxic heavy metals and environmentally sustainable phytoremediation technique for heavy metal polluted soils to offer widespread applicability of this green technology. Different strategies to enhance the bioavailability of heavy metals in the soil are also discussed shortly. It can be concluded that phytoremediation of heavy metal contaminated soils is a reliable tool and necessary for making the land resource accessible for crop production.

Removal and tolerance mechanism of Pb by a filamentous fungus: A case study

Currently, Pb pollution has become a severe environmental problem and filamentous fungi hold a promising potential for the treatment of Pb-containing wastewater. The present study showed that the strain Pleurotus ostreatus ISS-1 had a strong ability to tolerate Pb at high concentration and reached a removal rate of 53.7% in liquid media. Pb was removed by extracellular biosorption, intracellular bioaccumulation by mycelia, or precipitation with extracellular oxalic acids. On the cellular level, Pb was mainly distributed in the cell wall, followed by vacuoles and organelles. Fourier transform infrared spectroscopy (FTIR) analysis indicated that hydroxyl, amides, carboxyl, and sulfhydryl groups provided binding sites for Pb. Furthermore, Pb was found on the cell surface in the form of PbS and PbCO₃ through X-ray diffraction (XRD). Intracellular chelates such as thiol compounds and oxalic acid, as well as extracellular oxalic acid, might play an important role in the tolerance of Pb. In addition, isobaric tags for relative and absolute quantitation (iTRAQ) analysis showed that ATP-binding cassette (ABC) transporter, cytochrome P450, peroxisome, and the calcium signaling pathway might participate in both accumulation and detoxification of Pb. These results have successfully provided a basis for further developing Pb polluted water treatment technology by fungi.

The source of lead determines the relationship between soil properties and lead bioaccessibility

Lead (Pb) contaminated soil is of particular concern for infants and children due to their susceptibility to exposure, fast metabolic rates and rapidly developing neuronal systems. Determining the bioaccessibility of Pb in soils is critical in human health risk assessments, which can vary due to different soil properties and sources of Pb contamination. In this study, the potential relationships between soil properties and Pb bioaccessibility from various Pb sources including Pb contamination from mining (specifically, Broken Hill), three shooting ranges, a smelter and two industry sites (pottery and battery), were investigated using the Relative Bioavailability Leaching Procedure (RBALP). We found the following: (1) CEC, TOC, sand and silt content, and total Pb were significantly different (p < 0.05) between the two particle size fractions of < 2 mm and < 250 μm; (2) EC, CEC and total Pb were significantly correlated to Pb bioaccessibility (p < 0.05); and (3) soil analyses based on source of Pb demonstrated a strongly significant relationship between Pb bioaccessibility and soil properties (CEC, EC, clay content and total Pb) for mining soils from Broken Hill (r² = 0.86, p < 0.05, n = 18). These results demonstrated the influences of Pb contamination sources, soil properties and particle size fractions on Pb bioaccessibility as well as the prediction of Pb bioaccessibility using soil properties. The findings documented here will help in developing a predictive tool for human health risk assessment and the remediation of Pb contaminated soils.

Lead exposure to children from consumption of backyard chicken eggs

Backyard chicken ownership is rapidly increasing in urban areas in the United States, largely as a way to provide eggs for household consumption. Despite elevated levels of environmental lead contamination in many US cities, the role of backyard chicken eggs as a pathway for lead exposure, particularly for children, has received limited scrutiny. To characterize lead exposure from consumption of backyard chicken eggs for children and predict related effects on blood lead level (BLL), we conducted a cross-sectional study of backyard chicken owners in the Greater Boston area (n = 51). We interviewed participants regarding egg consumption by household members and collected backyard eggs (n = 201) and coop soil samples (n = 48) for analysis. Inductively coupled plasma mass spectrometry (ICP-MS) was used to evaluate lead concentration in homogenized eggs and an X-ray fluorescence (XRF) portable device was used to assess soil lead levels in the laboratory. We used the USEPA's Integrated Exposure Uptake Biokinetic Model for Lead in Children (IEUBK) to assess the relative contribution of backyard egg consumption to aggregate BLL in children. Four scenarios were developed in the IEUBK model to address variability in egg consumption rates and egg lead contamination. Lead was detected in egg samples from 98% of the households that provided egg samples. Mean household lead concentration was 0.10 μg/g (SD: 0.18). Egg lead concentrations ranged from below the limit of detection (0.0014 μg/g) to 1.798 μg/g (<1.4-1198 ppb). Egg lead levels were strongly positively correlated with lead concentration in coop soil (r = 0.64; p < 0.001). In modeled scenarios where a child < 7 years frequently ate eggs highly contaminated with lead, BLLs are predicted to increase by 0.9-1.5 μg/dL. In three other scenarios reflecting more moderate egg lead contamination and consumption rates, BLLs were predicted to increase from 0.1 to 0.8 μg/dL. Consumption of backyard chicken eggs can contribute to lead exposure in children. Soil lead remediation prior to chicken ownership may reduce lead exposure from backyard eggs.

The Fate of Chemical Pollutants with Soil Properties and Processes in the Climate Change Paradigm—A Review

Heavy metal(loid)s and organic contaminants are two major groups of pollutants in soils. The fate and exposure of such pollutants in soil depends on their chemical properties, speciation, and soil properties. Soil properties and processes that control the toxicological aspects of pollutants include temperature, moisture, organic matter, mineral fractions, and microbial activities. These processes are vulnerable to climate change associated with global warming, including increased incidences of extreme rainfall, extended dry periods, soil erosion, and a rise in sea level. Here we explain evidence that relates to the effects of climate change-driven soil processes on the mobility, transport, and storage of pollutants in soil. The review found that changes in climate could increase human exposure to soil contaminants mainly due to processes involving soil organic carbon (SOC), surface runoff, redox state, and microbial community. However, uncertainties remain in relation to the extent of contaminant toxicity to human health, which is linked to global change drivers.

Comparison of tolerance and biosorption of three trace metals (Cd, Cu, Pb) by the soil fungus Absidia cylindrospora

Trace metals cause deterioration of the soil and constitute a major concern for the environment and human health. Bioremediation could be an effective solution for the rectification of contaminated soils. Fungi could play an important role in biodegradation because of the morphology of their mycelium (highly reactive and extensive biological surface) and its physiology (high tolerance to many stresses, production of enzymes and secondary metabolites). Fungi can effectively biosequestrate, or biotransform many organic and inorganic contaminants into a non-bioavailable form. This experiment was designed to evaluate the tolerance and the biosorption abilities of the fungus Absidia cylindrospora against three trace metals: Cadmium (Cd), Copper (Cu), and Lead (Pb). Firstly, the tolerance of the strain was evaluated on metal-enriched malt extract agar (MEA). Secondly, the strain was exposed to trace metals, in a liquid malt extract medium. After 3 or 7 days of exposure, the quantities of absorbed and adsorbed metals were measured with Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). Biomass production and pH evolution were also evaluated during the test. Our experiment revealed differences between the three metals. In agar medium, Cd and Pb were better tolerated than Cu. In liquid medium, Cd and Pb were mostly absorbed whereas Cu was mostly adsorbed. A. cylindrospora biosorbed 14% of Cu, 59% of Pb and 68% of Cd when exposed for 3 days at 50 mg L^-1.

In vitro dermal bioaccessibility of selected metals in contaminated soil and mine tailings and human health risk characterization

Dermal exposure to contaminated sites has generally received less attention than oral/inhalation exposure due to limited exposure scenarios and less perceived potential for toxicity, however, the risk can be significant for specific contaminants and scenarios. The present study aims to (1) measure Cr, Ni, Pb, and Zn contamination in soil and mine tailings samples (n = 7), (2) determine the dermal bioaccessibility of these metals via in vitro tests using two synthetic sweat formulations (EN 1811; NIHS 96-10), and (3) obtain dermal absorbed doses (DADs) for children's and adults' exposure scenarios and compare them to derived dermal reference values. The NIHS 96-10 formulation yielded higher bioaccessibility values for all metals than EN 1811, possibly due to its lower pH. Zn had the highest bioaccessibility for both formulations whereas Cr had the lowest. There was some evidence of adsorption of initially mobilized Pb and Zn to soil with longer test times, resulting in slightly lower bioaccessibility after 8 h of testing with respect to 2 h. The calculated DADs showed that the risk for exposure was acceptable (DAD < derived dermal reference value) for all metals except for Cr(VI) considering exposure to two of the samples. The risk in the case of children's exposure scenario (play on contaminated medium) was significantly higher than the case for the adults' exposure scenario (exposure in industrial context). Additional bioaccessibility research is recommended on additional samples with differing properties/contamination profiles, on additional contaminants with high dermal affinity (especially As), and on the development/validation of in vitro dermal bioaccessibility tests.

Measurement of soil lead bioavailability and influence of soil types and properties: A review

Lead (Pb) is a widespread heavy metal which is harmful to human health, especially to young children. To provide a human health risk assessment that is more relevant to real conditions, Pb bioavailability in soils is increasingly employed in the assessment procedure. Both in vivo and in vitro measurements for lead bioavailability are available. In vivo models are time- consuming and expensive, while in vitro models are rapid, economic, reproducible, and reliable while involving more uncertainties. Uncertainties in various measurements create difficulties in accurately predicting Pb bioavailability, resulting in the unnecessary remediation of sites. In this critical review, we utilised available data from in vivo and in vitro studies to identify the key parameters influencing the in vitro measurements, and presented uncertainties existing in Pb bioavailability measurements. Soil type, properties and metal content are reported to influence lead bioavailability; however, the differences in methods for assessing bioavailability and the differences in Pb source limit one's ability to conduct statistical analyses on influences of soil factors on Pb bioavailability. The information provided in the review is fundamentally useful for the measurement of bioavailability and risk assessment practices.

Phytoremediation effect of Scirpus triqueter inoculated plant-growth-promoting bacteria (PGPB) on different fractions of pyrene and Ni in co-contaminated soils

At present, few reveal the mechanism of inoculation plants with PGPB to remediate PAH-metal co-contaminated soil by analyzing the chemical speciations of contaminants. This study investigated the influence of inoculation plants with PGPB on different fractions of pyrene and Ni in rhizospheric and non-rhizospheric soil. The results demonstrated that the addition of PGPB brought the extensive increase of FDA activities in pyrene-Ni co-contaminated soil. PGPB increased the resistance of plants in nickel and pyrene-Ni contaminated soil, but decreased the plant biomass in single pyrene contaminated soil. The addition of PGPB efficiently decreased bioaccessible fractions of pyrene and increased the bioavailability of Ni in both rhizospheric and non-rhizospheric soil. Although inoculation plants with PGPB significantly increased the accumulation of Ni in single Ni and pyrene-Ni co-contaminated soil, the poor bioavailability of Ni in rhizospheric soil still restricted the phytoremediation of the heavy metal. The presence of pyrene hindered the inoculated plant from accumulating Ni to some extent. On the contrary, the presence of Ni significantly promoted the degradation of pyrene in both rhizospheric and non-rhizospheric soil after inoculation plants with PGPB.

A meta-analysis to correlate lead bioavailability and bioaccessibility and predict lead bioavailability

Defining the precise clean-up goals for lead (Pb) contaminated sites requires site-specific information on relative bioavailability data (RBA). While in vivo measurement is reliable but resource insensitive, in vitro approaches promise to provide high-throughput RBA predictions. One challenge on using in vitro bioaccessibility (BAc) to predict in vivo RBA is how to minimize the heterogeneities associated with in vivo-in vitro correlations (IVIVCs) stemming from various biomarkers (kidney, blood, liver, urinary and femur), in vitro approaches and studies. In this study, 252 paired RBA-BAc data were retrieved from 9 publications, and then a Bayesian hierarchical model was implemented to address these random effects. A generic linear model (RBA (%)=(0.87±0.16)×BAc+(4.70±2.47)) of the IVIVCs was identified. While the differences of the IVIVCs among the in vitro approaches were significant, the differences among biomarkers were relatively small. The established IVIVCs were then applied to predict Pb RBA of which an overall Pb RBA estimation was 0.49±0.25. In particular the RBA in the residential land was the highest (0.58±0.19), followed by house dust (0.46±0.20) and mining/smelting soils (0.45±0.31). This is a new attempt to: firstly, use a meta-analysis to correlate Pb RBA and BAc; and secondly, estimate Pb RBA in relation to soil types.

Effect of alkyl polyglucoside and nitrilotriacetic acid combined application on lead/pyrene bioavailability and dehydrogenase activity in co-contaminated soils

At present, few research focus on the phytoremediation for organic pollutants and heavy metals enhanced by surfactants and chelate agents in the combined contaminated soils or sediments. In this study, the effect of a novel combined addition of alkyl polyglucoside (APG) and nitrilotriacetic acid (NTA) into pyrene and lead (Pb) co-contaminated soils on bioaccessiblity of pyrene/Pb and dehydrogenase activities (DHA) was studied. Through the comparison of the results with the alone and combined application, synergistic effect on bioaccessiblity of pyrene and Pb was found while APG and NTA was applied together. Results also indicated a significant promotion on the DHA in mixed addition of APG and NTA. In addition, correlation and principal component analysis were performed to better understand the relationship among APG/NTA, bioaccessiblity of pyrene/Pb and the DHA. Results showed that APG and NTA can affect DHA directly by themselves but also can affect DHA indirectly by changing bioaccessible pyrene and exchangeable Pb.

Predicting copper phytotoxicity based on pore-water pCu

The free ion activity and "biotic ligand" models predict that the free metal ion and other pore-water parameters describe terrestrial phytotoxicity. In this study, pore-water chemistry and measured Cu(2+) was used to describe phytotoxicity of cucumber (Cucumis sativa L) in 10 contrasting soils at different soil Cu loadings. Both soil solution Cu (Cu(pw)) and Cu(2+) successfully described the response variable for all ten soils with R(2) values of 0.73 and 0.66, respectively. Separation of soils as acid and alkaline and fitting separately showed that there was a strongly significant fit for both log Cu(2+) and log Cu(pw) in acidic soils (R(2) = 0.92 and 0.86, respectively) but weakly significant fit for alkaline soils. The pCu EC50 and EC10 values in all acidic soils for cucumber were 5.83 (6.03-5.63) and 7.53 (8.27-7.00), respectively. In our dataset alkaline soils need to be treated individually. In addition, pCu could be predicted based on pH and total concentration alone. Despite only 12 weeks 'ageing' there was quantitative agreement between pCu model from this study and predicted pCu from Sauvé et al. This agreement from studies performed independently indicates that, at least in the case of Cu(2+), the difference in an ageing period of ≥10 years appears minimal.