A methodological approach for the identification of arsenic bearing phases in polluted soils

A methodological approach is used to characterize arsenic pollution in three soils and to determine arsenic speciation and association with solid phases in three polluted soils. HPLC-ICP-MS was used for arsenic speciation analysis, SEM-EDS and XRD for physical characterization of arsenic pollution, and sequential chemical extractions to identify arsenic distribution. Arsenic was concentrated in the finest size fractions also enriched in iron and aluminium. Total arsenic concentrations in soils are close to 1%. Arsenic was mainly present as arsenate, representing more than 90% of total arsenic. No crystallised arsenic minerals were detected by XRD analysis. SEM-EDS observations indicated arsenic/iron associations. Modified Tessier's procedure showed that arsenic was mainly extracted from amorphous iron oxide phase. The results of this methodological approach lead to predict the formation of iron arsenates in the case of one of the studied soils while arsenic sorption on iron amorphous (hydr)oxides seemed to be the determinant in the two other soils.     

Fate and bioavailability of arsenic in organo-arsenical pesticide-applied soils. Part-I: incubation study

A laboratory incubation study was conducted to estimate geochemical speciation and in vitro bioavailability of arsenic as a function of soil properties. Two chemically-variant soil types were chosen, based on their potential differences with respect to arsenic reactivity: an acid sand with minimal arsenic retention capacity and a sandy loam with relatively high concentration of amorphous Fe/Al-oxides, considered a sink for arsenic. The soils were amended with dimethylarsenic acid (DMA) at three rates: 45, 225, and 450 mg/kg. A sequential extraction scheme was employed to identify the geochemical forms of arsenic in soils, which were correlated with the "in vitro" bioavailable fractions of arsenic to identify the most bioavailable species. Arsenic bioavailability and speciation studies were done at 0 time (immediately after spiking the soils with pesticide) and after four-months incubation. Results show that soil properties greatly impact geochemical speciation and bioavailability of DMA; soils with high concentrations of amorphous Fe/Al oxides retain more arsenic, thereby rendering them less bioavailable. Results also indicate that the use of organic arsenicals as pesticides in mineral soils may not be a safe practice from the viewpoint of human health risk.     

Effects of dissolution kinetics on bioaccessible arsenic from tailings and soils

Dissolution kinetics of arsenic from soils and tailings were studied under simulated gastrointestinal conditions to determine the effects of residence time, pH and soil composition on the bioaccessibility of arsenic. The samples were sieved to four particle size fractions from bulk to <45 μm, and included arsenic minerals, soils and tailings with total arsenic concentrations ranging from 19 to 420 00 mg kg⁻¹. The bioaccessible arsenic concentrations varied from 2.8 to 10 000 mg kg⁻¹, and the highest concentrations were associated with the smallest particle size fractions. Kinetic parameters were determined for each sample extracted under gastric conditions (pH = 1.8) followed by intestinal conditions (pH = 7.0). Under gastric pH conditions, dissolution appeared to be diffusion-controlled and followed an exponential curve, whereas a logarithmic or linear model was used to describe the mixed dissolution mechanisms observed under intestinal conditions. Nine of the 13 samples tested reached a steady state bioaccessible arsenic concentration within the 5-h physiologically-based extraction test (PBET). However the bioaccessible arsenic concentrations in four tailings samples increased significantly (p = 0.034) between the 5-h and the extended 24-h extraction under intestinal conditions. Since arsenic absorption may occur along the entire digestive tract, assessments based on the standard 5-h PBET extraction may not adequately estimate the risks associated with arsenic absorption in such cases. The slow dissolution kinetics associated with secondary arsenic minerals in some tailings samples may require extending the PBET extractions to longer periods, or extrapolating using the proposed kinetic models, to reach steady state concentrations in simulated gastrointestinal fluids.     

Phytoextraction by arsenic hyperaccumulator Pteris vittata L. from six arsenic-contaminated soils: Repeated harvests and arsenic redistribution

This greenhouse experiment evaluated arsenic removal by Pteris vittata and its effects on arsenic redistribution in soils. P. vittata grew in six arsenic-contaminated soils and its fronds were harvested and analyzed for arsenic in October, 2003, April, 2004, and October, 2004. The soil arsenic was separated into five fractions via sequential extraction. The ferns grew well and took up arsenic from all soils. Fern biomass ranged from 24.8 to 33.5 g plant(-1) after 4 months of growth but was reduced in the subsequent harvests. The frond arsenic concentrations ranged from 66 to 6,151 mg kg(-1), 110 to 3,056 mg kg(-1), and 162 to 2,139 mg kg(-1) from the first, second and third harvest, respectively. P. vittata reduced soil arsenic by 6.4-13% after three harvests. Arsenic in the soils was primarily associated with amorphous hydrous oxides (40-59%), which contributed the most to arsenic taken up by P. vittata (45-72%). It is possible to use P. vittata to remediate arsenic-contaminated soils by repeatedly harvesting its fronds.     

Sequential soil washing techniques using hydrochloric acid and sodium hydroxide for remediating arsenic-contaminated soils in abandoned iron-ore mines

Sequential washing techniques using single or dual agents [sodium hydroxide (NaOH) and hydrochloric acid (HCl) solutions] were applied to arsenic-contaminated soils in an abandoned iron-ore mine area. We investigated the best remediation strategies to maximize arsenic removal efficiency for both soils and arsenic-containing washing solution through conducting a series of batch experiments. Based on the results of a sequential extraction procedure, most arsenic prevails in Fe-As precipitates or coprecipitates, and iron exists mostly in the crystalline forms of iron oxide. Soil washing by use of a single agent was not effective in remediating arsenic-contaminated soils because arsenic extractions determined by the Korean standard test (KST) methods for washed soils were not lower than 6mg kg(-1) in all experimental conditions. The results of X-ray diffraction (XRD) indicated that iron-ore fines produced mobile colloids through coagulation and flocculation in water contacting the soils, containing dissolved arsenic and fine particles of ferric arsenate-coprecipitated silicate. The first washing step using 0.2M HCl was mostly effective in increasing the cationic hydrolysis of amorphous ferrihydrite, inducing high removal of arsenic. Thus, the removal step of arsenic-containing flocs can lower arsenic extractions (KST methods) of washed soils. Among several washing trials, alternative sequential washing using 0.2M HCl followed by 1M HCl (second step) and 1M NaOH solution (third step) showed reliable and lower values of arsenic extractions (KST methods) of washed soils. This washing method can satisfy the arsenic regulation of washed soil for reuse or safe disposal application. The kinetic data of washing tests revealed that dissolved arsenic was easily readsorbed into remaining soils at a low pH. This result might have occurred due to dominant species of positively charged crystalline iron oxides characterized through the sequential extraction procedure. However, alkaline extraction using NaOH was effective in removing arsenic readsorbed onto the surface of crystalline minerals. This is because of the ligand displacement reaction of hydroxyl ions with arsenic species and high pH conditions that can prevent readsorption of arsenic.     

A comparison of physiologically based extraction test (PBET) and single-extraction methods for release of Cu, Zn, and Pb from mildly acidic and alkali soils

In vitro digestion test can be applied to evaluate the bioaccessibility of soil metals by measuring the solubility of the metals in synthetic human digestive tract. Physiologically based extraction test (PBET), composed of sequential digestion of gastric and intestinal phase, is one of the frequently used in vitro digestion tests. In this study, the PBET was chosen to determine the bioaccessibility of Cu, Zn, and Pb in 14 mildly acidic and alkali (pH 5.87–8.30) soils. The phytoavailability of Cu, Zn, and Pb in the same soils was also measured using six single-extraction methods (0.1 M HNO₃, 0.4 M HOAc, 0.1 M NaNO₃, 0.01 M CaCl₂, 0.05 M EDTA, and 0.5 M DTPA). The extraction efficiencies of the methods were compared. The PBET had a strong ability to extract metals from soil, which was much greater than neutral salt extraction and close to dilute acid and complex extraction in spite of the last 2 h neutral intestinal digestion. The amounts of bioaccessible Cu, Zn, and Pb in the gastric phase and in the gastrointestinal phase were both largely determined by the total content of soil Cu, Zn, and Pb. But the results of gastrointestinal digestion reflected more differences resulting from element and soil types than those of gastric digestion did. It was noticed that most of variations in the amounts of soil Cu, Zn, and Pb extracted by EDTA were well explained by the total soil Cu, Zn, and Pb, as same as the PBET. Moreover, the solubility of Cu, Zn, and Pb in the gastric phase and gastrointestinal phase were all positively linearly correlated with the results of EDTA. It was suggested that EDTA extraction can be used to predict the bioaccessibility of Cu, Zn, and Pb in mildly acidic and alkali (pH?>?5.8) soils, and the PBET and EDTA could be applied to measure, in a certain extent, the bioaccessibility and phytoavailability of Cu, Zn, and Pb in mildly acidic and alkali (pH?>?5.8) soils at the same time.     

Arsenic Background Concentrations in Florida,U.S.A. Surface Soils: Determination and Interpretation

Background concentrations of soil arsenic have been used as an alternative soil cleanup criterion in many states in the U.S. This research addresses issues related to the interpretation of background concentrations of arsenic in near pristine soils in Florida. Total arsenic was measured in 448 taxonomic and geographic representative surface soil samples using USEPA Method 3052 (HCl-HNO 3 -HF, microwave digestion) and graphite furnace atomic absorption spectrophotometry analysis procedure. Values were log-normally distributed, with geometric mean and baseline concentration (defined as 95% of the expected range of background concentrations) providing the most satisfactory statistical results. An upper baseline concentration of 6.21 mg As/kg was estimated for undisturbed soils (n=267) compared to 7.63 mg As/kg for disturbed soils (n=181). Temporal trend of total soil arsenic concentrations from 1967 to 1989 paralleled decreased usage of arsenic in U.S. agriculture. Soil arsenic background concentrations were generally higher in south Florida than in north and central Florida, and associated with wet soils. Individual high arsenic sites were scattered throughout the state, but the most highly concentrated of these occurred in the Leon-Lee belt along the Ocala uplift district extending to the southwestern flatwoods district. Extrapolation of the data using a single arsenic value regardless of the taxonomic and geographical differences in soil arsenic distribution would underestimate potential arsenic contamination in upland soils.     

Arsenic accumulation by two brake ferns growing on an arsenic mine and their potential in phytoremediation

In an area near an arsenic mine in Hunan Province of south China, soils were often found with elevated arsenic levels. A field survey was conducted to determine arsenic accumulation in 8 Cretan brake ferns (Pteris cretica) and 16 Chinese brake ferns (Pteris vittata) growing on these soils. Three factors were evaluated: arsenic concentration in above ground parts (fronds), arsenic bioaccumulation factor (BF; ratio of arsenic in fronds to soil) and arsenic translocation factor (TF; ratio of arsenic in fronds to roots). Arsenic concentrations in the fronds of Chinese brake fern were 3-704 mg kg-1, the BFs were 0.06-7.43 and the TFs were 0.17-3.98, while those in Cretan brake fern were 149-694 mg kg-1, 1.34-6.62 and 1.00-2.61, respectively. Our survey showed that both ferns were capable of arsenic accumulation under field conditions. With most of the arsenic being accumulated in the fronds, these ferns have potential for use in phytoremediation of arsenic contaminated soils.     

Effects of organic matter and ageing on the bioaccessibility of arsenic

Arsenic-contaminated soils may pose a risk to human health. Redevelopment of contaminated sites may involve amending soils with organic matter, which potentially increases arsenic bioaccessibility. The effects of ageing on arsenic-contaminated soils mixed with peat moss were evaluated in a simulated ageing period representing two years, during which arsenic bioaccessibility was periodically measured. Significant increases (p = 0.032) in bioaccessibility were observed for 15 of 31 samples tested, particularly in comparison with samples originally containing >30% bioaccessible arsenic in soils naturally rich in organic matter (>25%). Samples where percent arsenic bioaccessibility was unchanged with age were generally poor in organic matter (average 7.7%) and contained both arsenopyrite and pentavalent arsenic forms that remained unaffected by the organic matter amendments. Results suggest that the addition of organic matter may lead to increases in arsenic bioaccessibility, which warrants caution in the evaluation of risks associated with redevelopment of arsenic-contaminated land.     

Concentrations and bioaccessibility of polycyclic aromatic hydrocarbons in wastewater-irrigated soil using in vitro gastrointestinal test

BACKGROUND, AIM, AND SCOPE: Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants and contribute to the pollution of soil environment. Soil ingestion is of increasing concern for assessing health risk from PAH-contaminated soils because soil ingestion is one of the potentially important pathways of exposure to environmental pollutants, particularly relevant for children playing at contaminated sites due to their hand-to-mouth activities. In vitro gastro-intestinal tests imitate the human digestive tract, based on the physiology of humans, generally more simple, less time-consuming, and especially more reproducible than animal tests. This study was conducted to investigate the level of PAH contamination and oral bioaccessibility in surface soils, using physiologically based in vitro gastro-intestinal tests regarding both gastric and small intestinal conditions. MATERIALS AND METHODS: Wastewater-irrigated soils were sampled from the metropolitan areas of Beijing and Tianjin, China, which were highly contaminated with PAHs. Reference soil samples were also collected for comparisons. At each site, four soils were sampled in the upper horizon at the depth of 0-20 cm randomly and were bulked together to form one composite sample. PAH concentrations and origin were investigated and a physiologically based in vitro test was conducted using all analytical grade reagents. Linear regression model was used to assess the relationship between total PAH concentrations in soils and soil organic carbon (SOC). RESULTS: A wide range of total PAH concentrations ranging from 1,304 to 3,369 mug kg(-1) in soils collected from different wastewater-irrigated sites in Tianjin, while ranging from 2,687 to 4,916 mug kg(-1) in soils collected from different wastewater-irrigated sites in Beijing, was detected. In general, total PAH concentrations in soils from Beijing sites were significantly higher than those from Tianjin sites, indicating a dominant contribution from both pyrogenic and petrogenic sources. Results indicated that the oral bioaccessibility of PAHs in small intestinal was significantly higher (from P < 0.05 to P < 0.001) than gastric condition. Similarly, the oral bioaccessibility of PAHs in contaminated sites was significantly higher (from P < or = 0.05 to P < 0.001) than in reference sites. Individual PAH ratios (three to six rings), a more accurate and reliable estimation about the emission sources, were used to distinguish the natural and anthropogenic PAH inputs in the soils. Results indicated that PAHs were both pyrogenic and petrogenic in nature. DISCUSSION: The identification of PAH sources and importance of in vitro test for PAH bioaccessibility were emphasized in this study. The oral bioaccessibility of individual PAHs in soils generally decreased with increasing ring numbers of PAHs in both the gastric and small intestinal conditions. However, the ratio of bioaccessibility of individual PAHs in gastric conditions to that in the small intestinal condition generally increased with increasing ring numbers, indicating the relatively pronounced effect of bile extract on improving the bioaccessibility of PAHs with relatively high ring numbers characterized by their high K ( ow ) values. Similarly, total PAH concentrations in soils were strongly correlated with SOC, indicating that SOC was the key factor determining the retention of PAHs in soils. CONCLUSIONS: Soils were contaminated with PAHs due to long-term wastewater irrigation. PAHs with two to six rings showed high concentrations with a significant increase over reference soils. Based on the molecular indices, it was suggested that PAHs in soils had both pyrogenic and petrogenic sources. It was also concluded that the oral bioaccessibility of total PAHs in the small intestinal condition was significantly higher than that in the gastric condition. Furthermore, the bioaccessibility of individual PAHs in soils generally decreased with the increasing ring numbers in both the gastric and small intestinal conditions. RECOMMENDATIONS AND PERSPECTIVES: It is suggested that more care should be given while establishing reliable soil criteria for PAHs, especially concerning the health of children who may ingest a considerable amount of PAH-contaminated soil via outdoor hand-to-mouth activities.     

Arsenic Background Concentrations in Florida,U.S.A. Surface Soils: Determination and Interpretation

Background concentrations of soil arsenic have been used as an alternative soil cleanup criterion in many states in the U.S. This research addresses issues related to the interpretation of background concentrations of arsenic in near pristine soils in Florida. Total arsenic was measured in 448 taxonomic and geographic representative surface soil samples using USEPA Method 3052 (HCl-HNO₃-HF, microwave digestion) and graphite furnace atomic absorption spectrophotometry analysis procedure. Values were log-normally distributed, with geometric mean and baseline concentration (defined as 95% of the expected range of background concentrations) providing the most satisfactory statistical results. An upper baseline concentration of 6.21 mg As/kg was estimated for undisturbed soils (n = 267) compared to 7.63 mg As/kg for disturbed soils (n = 181). Temporal trend of total soil arsenic concentrations from 1967 to 1989 paralleled decreased usage of arsenic in U.S. agriculture. Soil arsenic background concentrations were generally higher in south Florida than in north and central Florida, and associated with wet soils. Individual high arsenic sites were scattered throughout the state, but the most highly concentrated of these occurred in the Leon-Lee belt along the Ocala uplift district extending to the southwestern flatwoods district. Extrapolation of the data using a single arsenic value regardless of the taxonomic and geographical differences in soil arsenic distribution would underestimate potential arsenic contamination in upland soils.     

Effect of biosolid incorporation on arsenic distribution in Mollisol soils in central Chile

The effect of biosolid incorporation on arsenic distribution in Mollisol soils in central Chile was studied. Two soils were sequentially extracted for arsenic with a five-step method that accounts for the following arsenic forms: non-specifically adsorbed (F1), specifically adsorbed (F2), amorphous and poorly crystallized Fe and Al oxides (F3), well-crystallized Fe and Al oxides (F4) and residual (F5). The arsenic residual fraction was predominant in Pintué soil, whereas in Graneros soil, arsenic was mostly associated to amorphous Fe and Al oxides. Graneros soil exhibited a higher As(V) adsorbing capacity than Pintué soil, which relates to the higher clay and iron and aluminum oxides contents, confirming that these components participation is essential for the adsorption of this metalloid. Biosolid application at a rate of 100Mg ha(-1) caused an increase in arsenic bound to amorphous Fe and Al oxides and in the residual fraction, in Pintué soil. When Pintué soil was spiked with arsenic, aged for two months, and treated with biosolid (100Mg ha(-1)), the content of arsenic in the most labile fractions decreased, thus showing a favorable effect in its application to soils with few specific sites for arsenic adsorption. Arsenic speciation was carried out in the first two fractions of the sequential extraction procedure. As(V) was the main form in both fractions. Biosolid incorporation at a rate of 100Mg ha(-1) caused a significant increase in organic arsenic forms.     

Remediation of arsenic-contaminated soils and washing effluents

Laboratory experiments were conducted to determine the distribution of various arsenic species in tailings and soils. Other specific goal of the tests were to evaluate the extraction efficiency of arsenic using alkaline or acid washing, to determine optimum operational parameters of alkaline washing, and to evaluate the arsenic precipitation of washing effluents by pH adjustment or ferric chloride addition. Alkaline washing using sodium hydroxide was found to be favorable in removing arsenic from tailings or soils having a higher portion of arsenic in the operationally defined crystalline mineral fraction of crystalline oxide and amorphous aluminosilicates. This is due to the ligand displacement reaction of hydroxyl ions with arsenic species and high pH conditions that can prevent readsorption of arsenic because predominant negatively charged crystalline oxides do not attract the negatively charged oxyanions. For tailings, sodium hydroxide had 10-20 times higher extraction efficiencies than hydrochloric- or citric acid. The optimum concentration of sodium hydroxide for soil washing was determined to be 200 mM for all samples, while the optimum ratios were 10:1 and 5:1 for tailings and field/river sedimentary soils, respectively. The washing effluent of river soil was effectively treated by adjusting pH to 5-6 with hydrochloric acid, resulting in arsenic concentrations of <50 microgl(-1). In the case of field soil effluent, an addition of ferric chloride with a minimum mass ratio of 11 (Fe/As) was needed to reduce the arsenic below 50 microgl(-1).     

An interdisciplinary physical-chemical approach for characterization of arsenic in a calciner residue dump in Cornwall (UK)

During the later stages of hard-rock mining in Cornwall, UK, widespread processing and refining of arsenic in purpose-built calciners resulted in severe, localized contamination of soils with arsenic. Several physical-chemical techniques were applied to characterize arsenic in a calciner residue dump: X-ray powder diffraction (XRD), sequential extraction combined with hyphenated speciation methods, and X-ray absorption spectroscopic (XAS) methods such as XANES (X-ray absorption near-edge structure) and EXAFS (extended X-ray absorption fine structure). Arsenic was predominantly present in pentavalent form, bound to amorphous or poorly-crystalline hydrous oxides of Fe (probably alpha-hematite). A small amount of a non-classified crystalline iron arsenate phase was found, viz. Fe2(As(AsO4)3). There was also evidence for the presence of some arsenate bound to quartz (alpha-SiO2). The overall results make us believe that the normally assumed relative safety, from a mobility point of view, is questionable since only a small fraction of arsenic is found in a crystalline iron arsenate form.     

Arsenic in the soils of Zimapán, Mexico

Arsenic concentrations of 73 soil samples collected in the semi-arid Zimapán Valley range from 4 to 14 700 mg As kg(-1). Soil arsenic concentrations decrease with distance from mines and tailings and slag heaps and exceed 400 mg kg(-1) only within 500 m of these arsenic sources. Soil arsenic concentrations correlate positively with Cu, Pb, and Zn concentrations, suggesting a strong association with ore minerals known to exist in the region. Some As was associated with Fe and Mn oxyhydroxides, this association is less for contaminated than for uncontaminated samples. Very little As was found in the mobile water-soluble or exchangeable fractions. The soils are not arsenic contaminated at depths greater than 100 cm below the surface. Although much of the arsenic in the soils is associated with relatively immobile solid phases, this represents a long-term source of arsenic to the environment.     

Comparison of in vivo and in vitro methodologies for the assessment of arsenic bioavailability in contaminated soils

An in vivo swine assay was utilised for the determination of arsenic (As) bioavailability in contaminated soils. Arsenic bioavailability was assessed using pharmacokinetic analysis encompassing area under the blood plasma-As concentration time curve following zero correction and dose normalisation. In contaminated soil studies, As uptake into systemic circulation was compared to an arsenate oral dose and expressed as relative As bioavailability. Arsenic bioavailability ranged from 6.9+/-5.0% to 74.7+/-11.2% in 12 contaminated soils collected from former railway corridors, dip sites, mine sites and naturally elevated gossan soils. Arsenic bioavailability was generally low in the gossan soils and highest in the railway soils, ranging from 12.1+/-8.5% to 16.4+/-9.1% and 11.2+/-4.7% to 74.7+/-11.2%, respectively. Comparison of in vivo and in vitro (Simplified Bioaccessibility Extraction Test [SBET]) data from the 12 contaminated soils and bioavailability data collected from an As spiked soil study demonstrated that As bioavailability and As bioaccessibility were linearly correlated (in vivo As bioavailability (mgkg(-1))=14.19+0.93.SBET As bioaccessibility (mgkg(-1)); r(2)=0.92). The correlation between the two methods indicates that As bioavailability (in vivo) may be estimated using the less expensive, rapid in vitro chemical extraction method (SBET) to predict As exposure in human health risk assessment.     

Collateral benefits and hidden hazards of soil arsenic during abatement assessment of residential lead hazards

Abatement of soil-lead hazards may also reduce human exposure to other soil toxins, thereby achieving significant collateral benefits that are not accounted for today. This proposition was tested with the specific case of soil-arsenic, where 1726 residential soil samples were collected and analyzed for lead and arsenic. The study found that these two toxins coexisted in most samples, but their concentrations were weakly correlated, reflecting the differing sources for each toxin. Collateral benefits of 9% would be achieved during abatement of the lead-contaminated soils having elevated arsenic concentrations. However, a hidden hazard of 16% was observed by overlooking elevated arsenic concentrations in soils having lead concentrations not requiring abatement. This study recommends that soil samples collected under HUD programs should be collected from areas of lead and arsenic deposition and tested for arsenic as well as lead, and that soil abatement decisions consider soil-arsenic as well as soil-lead guidelines.     

The chemistry and behaviour of antimony in the soil environment with comparisons to arsenic: A critical review

This article provides a critical review of the environmental chemistry of inorganic antimony (Sb) in soils, comparing and contrasting findings with those of arsenic (As). Characteristics of the Sb soil system are reviewed, with an emphasis on speciation, sorption and phase associations, identifying differences between Sb and As behaviour. Knowledge gaps in environmentally relevant Sb data for soils are identified and discussed in terms of the limitations this imposes on understanding the fate, behaviour and risks associated with Sb in environmental soil systems, with particular reference to mobility and bioavailability.     

Protocol Development for Assessing Arsenic Background Concentrations in Florida Urban Soils

Knowledge of arsenic background concentrations in urban soils is important for making remediation decisions. The soil cleanup target level (SCTL) for arsenic in Florida lies within the range of arsenic background concentrations. The residential SCTL is also near the practical quantification limits using analytical procedures. Currently no standard protocols are available for determining arsenic background concentrations in urban soils, apart from site-specific cases. Therefore, a pilot study was conducted to develop and employ appropriate protocols to determine arsenic distribution in urban soils. This involved: site selection (e.g. size and sampling frame), sample collection (e.g. sampling technique), and statistical considerations (e.g. design). Factors such as ease of sample collection and maintaining anonymity of private properties were also considered as they influence the successful implementation of the study. Forty surface soil samples each were collected from five categories in three land use classes (residential-yard and right-of-way, commercial and public land-parks and public building), digested using EPA method 3051a and analysed using graphite furnace atomic absorption spectrometry. Experiences from the pilot study (e.g. complications during sample selection, digestion, data censoring etc.) were used in the development of the final protocol to be used in determining the distribution of arsenic in urban areas.     

Protocol Development for Assessing Arsenic Background Concentrations in Florida Urban Soils

Knowledge of arsenic background concentrations in urban soils is important for making remediation decisions. The soil cleanup target level (SCTL) for arsenic in Florida lies within the range of arsenic background concentrations. The residential SCTL is also near the practical quantification limits using analytical procedures. Currently no standard protocols are available for determining arsenic background concentrations in urban soils, apart from site-specific cases. Therefore, a pilot study was conducted to develop and employ appropriate protocols to determine arsenic distribution in urban soils. This involved: site selection (e.g. size and sampling frame), sample collection (e.g. sampling technique), and statistical considerations (e.g. design). Factors such as ease of sample collection and maintaining anonymity of private properties were also considered as they influence the successful implementation of the study. Forty surface soil samples each were collected from five categories in three land use classes (residential-yard and right-of-way, commercial and public land-parks and public building), digested using EPA method 3051a and analysed using graphite furnace atomic absorption spectrometry. Experiences from the pilot study (e.g. complications during sample selection, digestion, data censoring etc.) were used in the development of the final protocol to be used in determining the distribution of arsenic in urban areas.