Using phosphate amendments to reduce bioaccessible Pb in contaminated soils: A meta-analysis.

Measuring the reduction of in vitro bioaccessible (IVBA) Pb from the addition of phosphate amendments has been researched for more than 20 years. A range of effects have been observed from increases in IVBA Pb to almost 100% reduction. This study determined the mean change in IVBA Pb as a fraction of total Pb (AC) and relative to the IVBA Pb of the control soil (RC) with a random effects meta-analysis. Forty-four studies that investigated the ability of inorganic phosphate amendments to reduce IVBA Pb were identified through 5 databases. These studies were split into 3 groups: primary, secondary, and EPA Method 1340 based on selection criteria, with the primary group being utilized for subgroup analysis and meta-regression. The mean AC was approximately -12% and mean RC was approximately -25% for the primary and secondary groups. For the EPA Method 1340 group, the mean AC was -5% and mean RC was -8%. The results of subgroup analysis identified the phosphorous amendment applied and contamination source as having a significant effect on the AC and RC. Soluble amendments reduce bioaccessible Pb more than insoluble amendments and phosphoric acid is more effective than other phosphate amendments. Urban Pb contamination associated with legacy Pb-paint and tetraethyl Pb from gasoline showed lower reductions than other sources such as shooting ranges and smelting operations. Meta-regression identified high IVBA Pb in the control, low incubated soil pH, and high total Pb with the greater reductions in AC and RC. In order to facilitate comparisons across future remediation research, a set of minimum reported data should be included in published studies and researchers should use standardized in vitro bioaccessibility methods developed for P-treated soils. Additionally, a shared data repository should be created for soil remediation research to enhance available soil property information and better identify unique materials.

Predicting the modifying effect of soils on arsenic phytotoxicity and phytoaccumulation using soil properties or soil extraction methods.

Soils have the ability to modify contaminant bioavailability and toxicity. Prediction the modifying effect of soil on arsenic phytoaccumulation and phytoavailability using either soil property data or soil chemical extraction data in risk assessment of contaminated soil is highly desirable. In this study, plant bioassays important to ecological receptors, were conducted with 20 soils with a wide range in chemical and physical soil properties to determine the relationships between As measured by soil chemical extraction (soil pore water, Bray-1, sodium phosphate solution, hydroxylamine hydrochloride, and acid ammonium oxalate) or soil physico/chemical properties on arsenic phytotoxicity and phytoaccumulation. Soil pore water As and Bray-1 extracted As were significantly (P < 0.01) correlated with lettuce tissue As and those extractants and sodium phosphate were correlated with ryegrass tissue As. Hydroxylamine and acid ammonium oxalate extractions did not correlate with plant bioassay endpoints. Simple regression results showed that lettuce tissue relative dry matter growth (RDMG) was inversely related to tissue As concentration (r2 = 0.85, P < 0.01), with no significant relationship for ryegrass. Soil clay exhibited strong adsorption for As and significantly reduce tissue As for lettuce and ryegrass. In addition to clay content, reactive aluminum oxide (AlOx), reactive Fe oxide (FeOx) and eCEC was inversely related to ryegrass tissue As. Multiple regression equation was strongly predictive (r2 = 0.83) for ryegrass tissue As (log transformed) using soil AlOx, organic matter, pH, and eCEC as variables. Soil properties can greatly reduce contaminant phytoavailability, plant exposure and risk, which should be considered when assessing contaminant exposure and site-specific risk in As-contaminated soils.

Oral Bioavailability of As, Pb, and Cd in Contaminated Soils, Dust, and Foods based on Animal Bioassays: A Review.

Metal contamination in soil, dust, and food matrices impacts the health of millions of people worldwide. During the past decades, various animal bioassays have been developed to determine the relative bioavailability (RBA) of As, Pb, and Cd in contaminated soils, dust, and foods, which vary in operational approaches. This review discusses the strengths and weaknesses of different animal models (swine and mice), dosing schemes (single gavage dose, repeated gavage dose, daily repeated feeding, and free access to diet), and end points (blood, urine, and tissue) in metal-RBA measurement; compares metal-RBA obtained using mouse and swine bioassays, different dosing schemes, and different end points; and summarizes key findings on As-, Pb-, and Cd-RBA values in contaminated soils, dust, and foods. Future directions related to metal-RBA research are highlighted, including (1) comparison of metal-RBA determinations between different bioassays and different laboratories to ensure robust bioavailability data, (2) enhancing the metal-RBA database for contaminated dust and foods, (3) identification of physiological and physicochemical mechanisms responsible for variability in metal-RBA values, (4) formulation of strategies to decrease metal-RBA values in contaminated soils, dust, and foods, and (5) assessing the impacts of cocontaminants on metal-RBA measurement.

Arsenic Speciation of Contaminated Soils / Solid Wastes and Relative Oral Bioavailability in Swine and Mice.

Arsenic (As) is one of the most widespread, toxic elements in the environment and human activities have resulted in a large number of contaminated areas. However abundant, the potential of As toxicity from exposure to contaminated soils is limited to the fraction that will dissolve in the gastrointestinal system and be absorbed into systemic circulation or bioavailable species. In part, the release of As from contaminated soil to gastrointestinal fluid depends on the form of solid phase As also termed "As speciation." In this study, 27 As-contaminated soils and solid wastes were analyzed using X-ray absorption spectroscopy (XAS) and results were compared to in vivo bioavailability values determined using the adult mouse and juvenile swine bioassays. Arsenic bioavailability was lowest for soils that contained large amounts of arsenopyrite and highest for materials that contained large amounts of ferric arsenates. Soil and solid waste type and properties rather than the contamination source had the greatest influence on As speciation. Principal component analysis determined that As(V) adsorbed and ferric arsenates were the dominant species that control As speciation in the selected materials. Multiple linear regression (MLR) was used to determine the ability of As speciation to predict bioavailability. Arsenic speciation was predictive of 27% and 16% of RBA As determined using the juvenile swine and adult mouse models, respectively. Arsenic speciation can provide a conservative estimate of RBA As using MLR for the juvenile swine and adult mouse bioassays at 55% and 53%, respectively.

Using Public Health Data for Soil Pb Hazard Management in Ohio.

OBJECTIVES: To evaluate how frequently elevated soil lead (Pb) hazards (≥400 ppm Pb) were identified in existing blood Pb site investigations in Ohio. DESIGN: This study evaluated 3050 site investigations from the Ohio Department of Health for children with blood Pb levels at or above 10 µg dL that contained bare soil Pb data. SETTING: Data were collected from existing databases maintained by the Ohio Department of Health. PARTICIPANTS: All data were de-identified prior to analysis. The data used included blood Pb level test results for children (18 years or younger) in Ohio, with most data coming from children younger than 6 years. MAIN OUTCOME MEASURES: The main outcome measures were blood Pb levels and identified Pb concentrations in environmental media, including soil, paint, and dust. METHODS: Data were organized and summarized according to county. Summary statistics were generated on the basis of type of environmental media and county. RESULTS: Soil samples were collected in approximately 5% of all blood Pb cases in Ohio between 1999 and 2015. Median bare soil Pb was 1030 mg Pb kg (range, 0-345 021 mg Pb kg soil). Fifty-six of Ohio's 88 counties had at least 1 soil sample above 10 000 ppm (mg Pb kg). Multiple Pb hazards were identified, including bare soil (74% frequency), deteriorated exterior Pb paint (74%), deteriorated interior Pb paint (72%), and settled Pb dust (72%). Bare soil collected from identified dripline areas contained 2638 ppm Pb above soils collected from bare soil play areas (P = .02). Ninety assessments (3%) contained a bare soil hazard, with no other identified hazards. No trend was found comparing county mean or median Pb with county population. Previously identified high-risk counties for elevated blood Pb levels did not have an elevated prevalence of bare soil Pb hazards compared with other counties (P = .64). CONCLUSIONS: Site investigators should anticipate finding and managing elevated bare soil Pb in locations throughout Ohio. When communicating with the public about bare soil Pb hazards, practitioners and policy makers should emphasize the importance of addressing all potential Pb exposure sources. Findings demonstrate the importance of the individual home environment for exposure, as previously identified high-risk counties for elevated blood Pb levels were not different from other counties.

Management Options for Contaminated Urban Soils to Reduce Public Exposure and Maintain Soil Health.

Soil management in urban areas faces dual challenges of reducing public exposure to soil contaminants, such as lead (Pb) and polycyclic aromatic hydrocarbons, and maintaining soil function. This study evaluated three management options for an urban lot in Cleveland, OH, containing 185 to 5197 mg Pb kg and 0.28 to 5.50 mg benzo(a)pyrene kg. Treatment options included: (i) cap the site with a soil blend containing compost and beneficially reused dredged sediments, (ii) mix compost with the soil, and (iii) mix compost and sediments with the soil. The soil blend cap reduced surface soil Pb to 12.4 mg Pb kg and benzo(a)pyrene content to 0.99 ± 0.41 mg kg. Aggregate stability for 2- to 0.25-mm aggregates in the soil blend cap was 13% compared with the 38% aggregate stability in the urban soil. Mixing compost with the soil reduced benzo(a)pyrene content, but sample variability indicated that elevated spots likely remained exposed at the surface. Compost addition diluted soil Pb and increased aggregate stability to 60%. Mixing compost and sediments with the soil was the only management option accomplishing both management goals of reducing surface soil contaminants and maintaining soil health. For this combined mixing option, aggregate stability was 37%, soil Pb was 15 mg kg, and benzo(a)pyrene was 0.99 ± 0.09 mg kg. Food-grade oil addition did not increase benzo(a)pyrene degradation. Future studies should evaluate how incorporating soil blends in different soil types with a range of contaminants may offer a suitable long-term management option for urban soil contaminants.

Evaluating Public and Regulatory Acceptance for Urban Soil Management Approaches.

Regulators ( = 14) and the public ( = 30) were surveyed to compare how they perceived contaminated soil management strategies, including bioavailability assessments, using a mental models approach. Both groups proposed similar soil contamination definitions and agreed laboratory tests were needed to identify contaminants. When responding to open-ended questions about management options, regulators emphasized the risk assessment process, whereas the public noted specific treatment options. The majority of the public (68%) and regulators (86%) were concerned about particular contaminants. The public emphasized general contaminant categories, such as petroleum products and chemicals. Regulators listed specific compounds, including arsenic and dioxin. Both groups mentioned lead. Public and regulators had similar levels of agreement for soil removal ( = 0.96) and allowing soils with low bioavailability to remain in place ( = 0.66). The public were most opposed (43% disagree or strongly disagree) to using soil capping. Both groups were willing to consider using bioavailability assessments for contaminated soils. All regulators had heard of bioavailability, whereas 21 of the 24 (88%) public had not heard of this concept. Across all soil management options, the public tended to have higher rates of strongly disagree/disagree and neutral responses compared with regulators ( = 0.01). The neutral responses may indicate public ambivalence or insufficient information to respond about treatment options. Communication and public education efforts should emphasize the analytical process used to justify site-specific treatments. Additional surveys should evaluate public and regulator definitions of successful soil management and contaminant remediation in specific situations (i.e., case studies with specific contaminants and receptors of interest).

Soil solution interactions may limit Pb remediation using P amendments in an urban soil.

Lead (Pb) contaminated soils are a potential exposure hazard to the public. Amending soils with phosphorus (P) may reduce Pb soil hazards. Soil from Cleveland, OH containing 726 ± 14 mg Pb kg-1 was amended in a laboratory study with bone meal and triple super phosphate (TSP) at 5:1 P:Pb molar ratios. Soil was acidified, neturalized and re-acidified to encourage Pb phosphate formation. PRSTM-probes were used to evaluate changes in soil solution chemistry. Soil acidification did not decrease in vitro bioaccessible (IVBA) Pb using either a pH 1.5, 0.4 M glycine solution or a pH 2.5 solution with organic acids. PRSTM-probe data found soluble Pb increased 10-fold in acidic conditions compared to circumnetural pH conditions. In acidic conditions (p = 3-4), TSP treated soils increased detected P 10-fold over untreated soils. Bone meal application did not increase PRSTM-probe detected P, indicating there may have been insufficient P to react with Pb. X-ray absorption spectroscopy suggested a 10% increase in pyromorphite formation for the TSP treated soil only. Treatments increased soil electrical conductivity above 16 mS cm-1, potentially causing a new salinity hazard. This study used a novel approach by combining the human ingestion endpoint, PRSTM-probes, and X-ray absorption spectroscopy to evaluate treatment efficacy. PRSTM-probe data indicated potentially excess Ca relative to P across incubation steps that could have competed with Pb for soluble P. More research is needed to characterize soil solutions in Pb contaminated urban soils to identify where P treatments might be effective and when competing cations, such as Ca, Fe, and Zn may limit low rate P applications for treating Pb soils.

Phosphorus Amendment Efficacy for In Situ Remediation of Soil Lead Depends on the Bioaccessible Method.

A validated method is needed to measure reductions of in vitro bioaccessible (IVBA) Pb in urban soil remediated with amendments. This study evaluated the effect of in vitro extraction solution pH and glycine buffer on bioaccessible Pb in P-treated soils. Two Pb-contaminated soils (790-1300 mg Pb kg), one from a garden and one from a city lot in Cleveland, OH, were incubated in a bench scale experiment for 1 yr. Six phosphate amendments, including bone meal, fish bone, poultry litter, monoammonium phosphate, diammonium phosphate, and triple superphosphate, were added to containers at two application rates. Lead IVBA was assessed using USEPA Method 1340 and three modified versions of this method. Modifications included using solutions with pH 1.5 and 2.5 as well as using solutions with and without 0.4 mol L glycine. Soil amendments were ineffective in reducing IVBA Pb in these soils as measured by pH 1.5 with glycine buffer. The greatest reductions in IVBA Pb, from 5 to 26%, were found using pH 2.5 extractions. Lead mineral results showed several soil amendments promoted Pb phosphate formation, an indicator of remediation success. A significant negative linear relationship between reduction in IVBA Pb and Pb-phosphate formation was found only for pH 2.5 without glycine extraction solution. A modified USEPA Method 1340 without glycine and using pH 2.5 has the potential to predict P soil treatment efficacy and reductions in bioavailable Pb.

Bioaccessibility tests accurately estimate bioavailability of lead to quail.

Hazards of soil-borne lead (Pb) to wild birds may be more accurately quantified if the bioavailability of that Pb is known. To better understand the bioavailability of Pb to birds, the authors measured blood Pb concentrations in Japanese quail (Coturnix japonica) fed diets containing Pb-contaminated soils. Relative bioavailabilities were expressed by comparison with blood Pb concentrations in quail fed a Pb acetate reference diet. Diets containing soil from 5 Pb-contaminated Superfund sites had relative bioavailabilities from 33% to 63%, with a mean of approximately 50%. Treatment of 2 of the soils with phosphorus (P) significantly reduced the bioavailability of Pb. Bioaccessibility of Pb in the test soils was then measured in 6 in vitro tests and regressed on bioavailability: the relative bioavailability leaching procedure at pH 1.5, the same test conducted at pH 2.5, the Ohio State University in vitro gastrointestinal method, the urban soil bioaccessible lead test, the modified physiologically based extraction test, and the waterfowl physiologically based extraction test. All regressions had positive slopes. Based on criteria of slope and coefficient of determination, the relative bioavailability leaching procedure at pH 2.5 and Ohio State University in vitro gastrointestinal tests performed very well. Speciation by X-ray absorption spectroscopy demonstrated that, on average, most of the Pb in the sampled soils was sorbed to minerals (30%), bound to organic matter (24%), or present as Pb sulfate (18%). Additional Pb was associated with P (chloropyromorphite, hydroxypyromorphite, and tertiary Pb phosphate) and with Pb carbonates, leadhillite (a lead sulfate carbonate hydroxide), and Pb sulfide. The formation of chloropyromorphite reduced the bioavailability of Pb, and the amendment of Pb-contaminated soils with P may be a thermodynamically favored means to sequester Pb. Environ Toxicol Chem 2016;35:2311-2319. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US Government work and, as such, is in the public domain in the United States of America.

Bioavailability-Based In Situ Remediation To Meet Future Lead (Pb) Standards in Urban Soils and Gardens.

Recently the Centers for Disease Control and Prevention lowered the blood Pb reference value to 5 µg/dL. The lower reference value combined with increased repurposing of postindustrial lands are heightening concerns and driving interest in reducing soil Pb exposures. As a result, regulatory decision makers may lower residential soil screening levels (SSLs), used in setting Pb cleanup levels, to levels that may be difficult to achieve, especially in urban areas. This paper discusses challenges in remediation and bioavailability assessments of Pb in urban soils in the context of lower SSLs and identifies research needs to better address those challenges. Although in situ remediation with phosphate amendments is a viable option, the scope of the problem and conditions in urban settings may necessitate that SSLs be based on bioavailable rather than total Pb concentrations. However, variability in soil composition can influence bioavailability testing and soil amendment effectiveness. More data are urgently needed to better understand this variability and increase confidence in using these approaches in risk-based decision making, particularly in urban areas.

Modeling spatial patterns in soil arsenic to estimate natural baseline concentrations.

Arsenic in soil is an important public health concern, but risk-based toxicity regulatory standards derived from laboratory studies should also consider concentrations measured away from obvious contamination (i.e., baseline concentrations that approximate natural background) to avoid unnecessary remediation burdens on society. We used soil and stream sediment samples from the USGS National Geochemical Survey to assess the spatial distribution of As over a 1.16 × 10 km area corresponding to the state of Ohio. Samples were collected at 348 soil and 144 stream sites at locations selected to minimize anthropogenic inputs. Total As was measured by sodium peroxide fusion with subsequent dissolution using concentrated HCl and analysis using hydride-generation atomic absorption spectrometry. Arsenic in the soil and streambed samples ranged from 2.0 to 45.6 mg kg. Sequential Gaussian simulation was used to map the expected concentration of As and its uncertainty. Five areas of elevated concentration, greater than the median of 10 mg kg, were identified, and relationships to geologic parent materials, glacial sedimentation, and soil conditions interpreted. Arsenic concentrations <4 mg kg were rare, >10 mg kg common, and >20 mg kg not unusual for the central and west central portions of Ohio. Concentrations typically exceeded the soil As human generic screening level of 0.39 mg kg, a value corresponding to an increase in cancer risk of 1 in 1,000,000 for soil ingestion. Such results call into question the utility of the USEPA and similarly low soil screening levels. The contrast between laboratory screens and concentrations occurring in nature argue for risk assessment on the basis of baseline concentrations.

What is required for the validation of in vitro assays for predicting contaminant relative bioavailability? Considerations and criteria.

A number of studies have shown the potential of in vitro assays to predict contaminant in vivo relative bioavailability in order to refine human health exposure assessment. Although the term 'validated' has been used to describe the goodness of fit between in vivo and in vitro observations, its misuse has arisen from semantic considerations in addition to the lack of defined criteria for establishing performance validation. While several internal validation methods may be utilised, performance validation should preferably focus on assessing the agreement of model predictions with a set of data which are independent of those used to construct the model. In order to achieve robust validated predictive models, a number of parameters (e.g. size of data set, source of independent soils, contaminant concentration range, animal model, relative bioavailability endpoint) need to be considered in addition to defined criteria for establishing performance validation which are currently lacking.

Bioaccessible and non-bioaccessible fractions of soil arsenic.

In order for in vitro methods to become widely accepted as tools that accurately assess soil arsenic (As) exposure through the oral ingestion pathway, a better understanding is needed regarding which fractions of soil As are being measured in the in vitro extraction. The objective of the current study is to (1) identify in vitro bioaccessible (IVBA) and non-IVBA fractions of soil As using sequential extraction; and (2) determine the sorptive phases of soil in non-IVBA As soil fractions. Nineteen soils with a range of soil properties were spiked with 250 mg/kg of sodium arsenate and aged. In vitro bioaccessible As (IVBA As) was then determined using The Ohio State University in vitro gastrointestinal method (OSU-IVG), and soil As was fractionated using sequential extraction into: (F1) non-specifically sorbed; (F2) specifically sorbed; (F3) amorphous and poorly crystalline oxides of Fe and Al; (F4) well-crystallized oxides of Fe and Al and residual As phases. The IVBA As across the 19 soil ranged from 0.36 to 2.75 mmol/kg (12 to 86%) with a mean of 1.26 mmol/kg (42%) in the gastric phase and from 0.39 to 2.80 mmol/kg (13 to 87%) in the intestinal phase with a mean of 1.32 mmol/kg (43%). The results of the sequential extraction showed that IVBA As extracted by the OSU-IVG is the As present in the first two fraction (F1 and F2) of the sequential extraction. In the non-IVBA fractions, highly significant relationships (P < 0.01) exist between F3 As and log transformed F3 Fe (r (2) = 0.74), but not F3 Al. In addition, the gastric extraction dissolves a significant fraction of soil Al, but not soil Fe, therefore As sorbed to Al oxides likely contributed to IVBA As and is accounted for in the F2 fraction of the sequential extraction. In vitro methods that demonstrate the ability to extract the similar soil fractions that occur in vivo across a wide range of soil types and As-contaminant sources is an important criteria for in vitro method validation. Further research that includes soils with multiple As-contaminant sources (mining, pesticide, etc.), soil As fractionation, and in vivo bioavailability is needed in order to determine if F1+F2 are the bioavailable As fractions in soils that vary in total As content and sorbed As species.

Variability of bioaccessibility results using seventeen different methods on a standard reference material, NIST 2710.

Bioaccessibility is a measurement of a substance's solubility in the human gastro-intestinal system, and is often used in the risk assessment of soils. The present study was designed to determine the variability among laboratories using different methods to measure the bioaccessibility of 24 inorganic contaminants in one standardized soil sample, the standard reference material NIST 2710. Fourteen laboratories used a total of 17 bioaccessibility extraction methods. The variability between methods was assessed by calculating the reproducibility relative standard deviations (RSDs), where reproducibility is the sum of within-laboratory and between-laboratory variability. Whereas within-laboratory repeatability was usually better than (<) 15% for most elements, reproducibility RSDs were much higher, indicating more variability, although for many elements they were comparable to typical uncertainties (e.g., 30% in commercial laboratories). For five trace elements of interest, reproducibility RSDs were: arsenic (As), 22-44%; cadmium (Cd), 11-41%; Cu, 15-30%; lead (Pb), 45-83%; and Zn, 18-56%. Only one method variable, pH, was found to correlate significantly with bioaccessibility for aluminum (Al), Cd, copper (Cu), manganese (Mn), Pb and zinc (Zn) but other method variables could not be examined systematically because of the study design. When bioaccessibility results were directly compared with bioavailability results for As (swine and mouse) and Pb (swine), four methods returned results within uncertainty ranges for both elements: two that were defined as simpler (gastric phase only, limited chemicals) and two were more complex (gastric + intestinal phases, with a mixture of chemicals).

Application of ridge regression to quantify marginal effects of collinear soil properties on phytoaccumulation of arsenic, cadmium, lead, and zinc.

Soil properties that mitigate hazardous effects of environmental contaminants through soil chemical sequestration should be considered when evaluating ecological risk from terrestrial contamination. The objective of this research was to identify predominant soil chemical/physical properties that modify phytoaccumulation of As, Cd, Pb, and Zn to the non-hyperaccumulating higher plants: Alfalfa (Medicago sativa L.), perennial ryegrass (Lolium perenne L.), and Japanese millet (Echinochloa crusgalli L.). Transmission coefficients were estimated from a dose-response experiment with the use of aboveground tissue contaminant concentrations and correlated with selected soil property measurements to develop statistical prediction models for soil-specific adjustments to ecological risk assessments. Significant correlations between soil properties and transmission coefficients were observed for all four contaminants. Intercorrelation was also observed among soil properties, including cation exchange capacity (CEC) and soil pH (p = 0.035), CEC and total clay (p = 0.030), organic carbon (OC) and total clay content (p = 0.085), reactive iron oxides (FeOX) and OC (p = 0.078), and reactive Mn oxide (MnOX) and total clay content (p < 0.001). Ridge regression, a technique that suppresses the effects of multicollinearity and enables prediction, was used to assess the marginal contributions of soil properties found to mitigate phytoaccumulation. Prediction models were developed for all four contaminants. Significant variables were FeOX for As or pH, OC, CEC, clay content, or a combination of factors for cationic metal models. Ridge regression provides a powerful alternative to conventional multiple regression techniques for ecotoxicological studies when intercorrelated predictors are experimentally unavoidable, as with soil properties.

Application of ridge regression to quantify marginal effects of collinear soil properties on phytotoxicity of arsenic, cadmium, lead, and zinc.

Soil properties that the mitigate hazardous effects of environmental contaminants through soil chemical sequestration should be considered when evaluating ecological risk from terrestrial contamination. The objective of the present research was to identify predominant soil chemical and physical properties that modify the phytotoxicity of As, Cd, Pb, and Zn to the nonhyperaccumulating higher plant perennial ryegrass (Lolium perenne L.). Phytotoxicity parameters were estimated from a dose-response experiment using the aboveground dry matter growth endpoint and were correlated with an assortment of relevant soil property measurements, with the ultimate goal of developing statistical prediction models for soil-specific adjustments to ecological risk assessments. Significant correlations between soil properties and phytotoxicity estimates were observed for all four contaminants; however, intercorrelation was observed among soil properties, necessitating an alternative to the conventional multiple regression commonly used by ecotoxicologists. Ridge regression, a regression-based technique that suppresses the effects of multicollinearity and enables prediction, was used to assess the marginal contributions of all properties found to mitigate phytotoxicity. Ridge regression models are presented along with two common conventional regression methods and are collectively discussed within the context of the mitigating effects of soil properties on metal/metalloid phytotoxicity. Ridge regression appears to be a powerful alternative to conventional multiple regression for ecotoxicological studies when intercorrelation among predictors is experimentally unavoidable, such as with soil properties.

Linking solid phase speciation of Pb sequestered to birnessite to oral Pb bioaccessibility: implications for soil remediation.

Lead (Pb) sorption onto oxide surfaces in soils may strongly influence the risk posed from incidental ingestion of lead-contaminated soils. In this study, Pb was sorbed to a model soil mineral, birnessite, and was placed in a simulated gastrointestinal tract (in vitro) to simulate the possible effects of ingestion of a soil contaminated with Pb. The changes in Pb speciation were determined using extended X-ray absorption fine structure and X-ray absorption near edge spectroscopy. Birnessite has a very high affinity for Pb with a sorption maximum of 0.59 mol Pb kg(-1) (approximately 12% Pb sorbed by mass) in which there was no detectable bioaccessible Pb (< 0.002%). Surface speciation of the birnessite Pb was determined to be a triple corner sharing complex in the birnessite interlayer. Lead sorbed to Mn oxide in contaminated media will have a very low (approximately equal to 0) Pb bioaccessibility and present little risk associated with incidental ingestion of soil. These results suggest that birnessite, and other Mn oxides would be powerful remediation tools for Pb-contaminated media because of their high affinity for Pb.

Phenanthrene release from natural organic matter surrogates under simulated human gastrointestinal conditions.

The aliphatic region of natural organic matter (NOM) can retain polycyclic aromatic hydrocarbons (PAH) due to the presence of non-polar binding sites. Thus NOM may act as a vehicle for entry of PAH into the gastrointestinal system in man and animals. In this study, the release of phenanthrene from the aliphatic NOM surrogates cutin and cutan was measured under simulated human gastrointestinal formulations using three treatments designed to simulate the biological and chemical conditions of the gastrointestinal environment. The three experimental treatments were composed of fecal microorganisms, chyme, and chyme+fecal microorganisms. Water was used as a control treatment. Phenanthrene laden biopolymer and a C18 membrane were immersed in each treatment. Phenanthrene was extracted from each membrane and measured with HPLC. Membrane-associated phenanthrene was taken to represent the fraction that had desorbed from the biopolymer. Cutin was found to yield an average phenanthrene release 55% higher than cutan (94% vs. 39%). A significant decrease (p<0.05) in phenanthrene release was observed in both the chyme and chyme+fecal microorganism treatments as compared to the water treatment (control). The presence of enteric microorganisms did not significantly influence phenanthrene release and did not reduce phenanthrene bioaccessibility in gastrointestinal chyme. Over 80% of the phenanthrene in cutin was recovered in the C18 matrix and its relative amount was uninfluenced by the treatments. For cutan, only 25-50% of the phenanthrene was recovered, suggesting that cutin-associated phenanthrene was more loosely bound. These data demonstrate that the fractions of NOM retained phenanthrene to a varying extent and thus the predictions of phenanthrene bioavailability should also be assessed on the basis of the constituents of the NOM matrix.