Fractionation, Bioaccessibility, and Risk Assessment of Heavy Metals in the Soil of an Urban Recreational Area Amended with Composted Sewage Sludge

Evolution of Cu and Zn speciation in agricultural soil amended by digested sludge over time and repeated crop growth

Metals such as Zn and Cu present in sewage sludge applied to agricultural land can accumulate in soils and potentially mobilise into crops. Sequential extractions and X-ray absorption spectroscopy results are presented that show the speciation changes of Cu and Zn sorbed to anaerobic digestion sludge after mixing with soils over three consecutive 6-week cropping cycles, with and without spring barley (Hordeum vulgare). Cu and Zn in digested sewage sludge are primarily in metal sulphide phases formed during anaerobic digestion. When Cu and Zn spiked sludge was mixed with the soil, about 40% of Cu(I)-S phases and all Zn(II)-S phases in the amended sludge were converted to other phases (mainly Cu(I)-O and outer sphere Zn(II)-O phases). Further transformations occurred over time, and with crop growth. After 18 weeks of crop growth, about 60% of Cu added as Cu(I)-S phases was converted to other phases, with an increase in organo-Cu(II) phases. As a result, Cu and Zn extractability in the sludge-amended soil decreased with time and crop growth. Over 18 weeks, the proportions of Cu and Zn in the exchangeable fraction decreased from 36% and 70%, respectively, in freshly amended soil, to 28% and 59% without crop growth, and to 24% and 53% with crop growth. Overall, while sewage sludge application to land will probably increase the overall metal concentrations, metal bioavailability tends to reduce over time. Therefore, safety assessments for sludge application in agriculture should be based on both metal concentrations present and their specific binding strength within the amended soil.

Long-term agricultural reuse of treated wastewater and sewage sludge: developing a Time to Critical Content Index for metal species

This study evaluates the sustainability of spreading wastewater or sewage sludge on agricultural land, balancing benefits with contamination risks. Conventional ecological risk indices often fail to address the long-term accumulation of metals in soils. We investigate the feasibility of spreading based on current knowledge of potentially contaminating metals and their behavior in soil. We analyzed the speciation of metals (Ag, Cd, Co, Cr, Cu, Ni, Pb, Ti, Zn) through sequential extraction in sludge, treated wastewater, and soils after 14 years of application of sewage sludge and treated wastewater issued from an Algerian wastewater treatment plant. We introduce a Time to Critical Content Index (TCCI) that calculates the time required to reach critical levels of potentially mobile metals, considering total metal content and speciation. The TCCI takes into account product knowledge, soil characteristics, metal behavior, ecological/toxicological thresholds, and regulations. Applied to our case study, the TCCI indicates that spreading sewage sludge can continue despite metal contents exceeding regulatory ceiling values. The index serves as a precautionary measure, adaptable to evolving knowledge, providing a comprehensive framework for sustainable agricultural practices.

Oral bioaccessibility of PTEs in soils: A review of data, influencing factors and application in human health risk assessment

Understanding the behavior of metal(loi)ds transported from soil to humans is critical for human health risk assessment (HHRA). In the last two decades, extensive studies have been conducted to better assess human exposure to potentially toxic elements (PTEs) by estimating their oral bioaccessibility (BAc) and quantifying the influence of different factors. This study reviews the common in vitro methods used to determine the BAc of PTEs (in particular As, Cd, Cr, Ni, Pb, and Sb) under specific conditions (particularly in terms of the particle size fraction and validation status against an in vivo model). The results were compiled from soils derived from various sources and allowed the identification of the most important influencing factors of BAc (using single and multiple regression analyses), including physicochemical soil properties and the speciation of the PTEs in question. This review presents current knowledge on integrating relative bioavailability (RBA) in calculating doses from soil ingestion in the HHRA process. Depending on the jurisdiction, validated or non-validated bioaccessibility methods were used, and risks assessors applied different approaches: (i) using default assumptions (i.e., RBA of 1); (ii) considering that bioaccessibility value (BAc) accurately represents RBA (i.e., RBA equal to BAc); (iii) using regression models to convert BAc of As and Pb into RBA as proposed by the USA with the US EPA Method 1340; or (iv) applying an adjustment factor as proposed by the Netherlands and France to use BAc from UBM (Unified Barge Method) protocol. The findings from this review should help inform risk stakeholders about the uncertainties surrounding using bioaccessibility data and provide recommendations for better interpreting the results and using bioaccessibility in risk studies.

Respiratory bioaccessibility and solid phase partitioning of potentially harmful elements in urban environmental matrices

Studies regarding the role of geochemical processes in urban environmental matrices (UEM) and their influence on respiratory bioaccessibility in humans are scarce in humid tropical regions, especially in Brazil. Contaminated UEM are potentially hazardous to humans if particles <10 μm in diameter are inhaled and reach the tracheobronchial region. In this study, we evaluated samples collected in Brazilian UEMs with a large environmental liability left by former mining industries and in a city with strong industrial expansion. UEM samples were classified into soil, sediment and mine tailings according to the characteristics of the collection sites. The respiratory bioaccessibility of potentially harmful elements (PHE) was evaluated using artificial lysosomal fluid (ALF, pH 4.5), and the BCR-sequential extraction was performed to evaluate how the respiratory bioaccessibility of the PHE was related to the solid phase partitioning. The bioaccessible fraction (BAF) ranged from 54 to 98% for Cd; 21-89% for Cu; 46-140% for Pb, 35-88% for Mn and; 41-84% for Zn. The average BAF of the elements decreased in the following order: Soil: Cd > Pb > Mn > Zn > Cu; Tailing: Pb > Cd > Zn > Mn > Cu; and Sediments: Pb > Mn > Cd > Zn > Cu. BCR-fractions were useful to predict the PHE bioaccessibility (R² = 0.79-0.98), thus suggesting that particle geochemistry and mineralogy can influence PHE behaviour in the pulmonary fluid. Therefore, this approach provides a combination of quantitative and qualitative data, which allows us to carry out a more realistic assessment of the current situation of the potentially contaminated site and possible alternatives for decision making by the stakeholders.

Relationship between Urban Green Spaces and Cancer: A Scoping Review

This scoping study aims to explore the relationships between urban green spaces (UGSs) and the onset, remission and recovery of cancer. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) extension for scoping reviews (protocol published in 2018). Eligibility criteria for papers were: (1) to be concerned with UGSs, (2) reporting effects of UGSs on cancer-related outcomes including direct or indirect measures, (3) reporting randomized controlled trials, prospective cohort studies, case studies, observational studies, non-comparative studies, (4) in English or French. The search covered primary studies in the published and unpublished (grey) literatures searching by hand and electronic databases (MEDLINE, Green File, Cumulative Index to Nursing and Allied Health Literature and ScienceDirect). Among 1703 records screened by two reviewers independently, 29 were included for qualitative synthesis. We classify the cancers concerned and the effects reported i.e., protective effect, risk or without association. The most investigated cancers are bladder, breast and lung cancer. Our study also identified contributing factors and their mediating effects between UGSs and cancer. Even though the strength of the evidence of the associations between UGSs and cancer is still weak due to the low number of studies and their design, results highlight the wide variety of possible mediating factors between the use of green spaces and cancer occurrence, remission and/or prevention. Knowledge gaps and future research perspectives should be oriented to qualitative research on protective factors with an attention to equity in UGS access and use.

Trace elements in two particle size fractions of urban soils collected from playgrounds in Bratislava (Slovakia)

Today, it is proven that the contaminated urban soils are hazardous for the human health. Soil substrates of playgrounds call for special research as they are places where children are directly exposed to soil contaminants. Therefore, the objective of this work was to measure the pseudo-total contents and bioaccessibility of several metals and metalloids (As, Bi, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Sb, Sn, V, Zn) in two grain sizes (< 150 μm and < 50 μm) of playground soils in Bratislava city (the capital of Slovakia). The content of metal(loid)s in the soils was controlled by a number of factors, with their increased contents (above 75% percentile or higher) at sites influenced by point sources of pollution (industry and agriculture) or at old sites located in the city centre. Cobalt, Cr, Fe, Mn, Ni and V had relatively uniform contents in soils compared to the other elements. As regression modelling with a categorical variable confirmed, the age of urban areas influenced the accumulation of As, Bi, Cd, Cu, Hg, Pb, Sb and Sn in playground soils. Exploratory statistical techniques with compositionally transformed data (principal component analysis, cluster analysis and construction of symmetric coordinates for correlation analysis) divided trace elements into the two main groupings, Co, Cr, Fe, Mn, Ni, V and Bi, Cd, Cu, Hg, Pb, Sb, Sn, Zn. Median concentrations of the elements in smaller soil grains (< 50 μm) were significantly higher than in coarser grains (< 150 μm). Cobalt, Cu, Mn, Pb, Sn and Zn had significantly higher bioaccessible proportions (% of the pseudo-total content) in < 50 μm soil size than in < 150 μm; however, the same order of bioaccessibility was achieved in both grain sizes. The highest bioaccessibility had Cd, Cu, Pb and Zn (~ 40% and more), followed by Co, As, Mn, Sb (18-27%), Hg, Ni, Sn (10-12%) and finally Cr, Fe and V (less than 4%). The hazard index and carcinogenic risk values were higher in < 50 μm than in < 150 μm and significantly decreased in the two soil sizes when the bioaccessibility results were included in the health hazard calculation.

In vitro lung and gastrointestinal bioaccessibility of potentially toxic metals in Pb-contaminated alkaline urban soil: The role of particle size fractions

Potentially toxic metals (PTMs), associated with different size particles in soil, may play an important role in adverse health effect and risk for human. The objective is to evaluate the lung and gastrointestinal bioaccessibility and risk of PTMs in Pb-contaminated alkaline urban soil depending on the particle size fractions. The size fractions of 50-250 μm, 5-50 μm, 1-5 μm, <1 μm in Pb-contaminated alkaline urban soil from Baoji Heavy Industrial Base City, NW China, were screened by Sequential Wet Sieving Separation Procedure (SWSSP) based on Stokes' Law. The concentrations of 9 potentially toxic metals (As, Ba, Co, Cr, Cu, Mn, Ni, Pb and Zn) in each particle size fractions were characterized by ICP-OES and ICP-MS, and the in vitro bioaccessibility dependent of size fractions were evaluated by the simulation fluids of Artificial Lysosomal Fluid (ALF) and Gamble for lung, PBET, SBET, IVG, SBRC, UBM for gastric and intestinal, respectively. Health risks were assessed considering simulated external exposure using intestinal and lung bioaccessibility. The lung and gastrointestinal bioaccessibility and exposure risks of PTMs in fine particle size (i.e. <1 μm) was higher than larger particle size fractions (i.e. 50-250 μm, 5-50 μm, 1-5 μm), however, some different variations of bioaccessibility observed the simulation fluids and time dependent. In case of single PTMs, the lung bioaccessibilities of PTMs in ALF were higher than those in Gamble fluids, most prominent in Co, Cu, Mn and Zn, while the gastrointestinal [G + I] bioaccessibility of PTMs was less than those in gastric [G], like Cu, Mn, Pb and Zn mostly. The non-carcinogenic risks of these PTMs to children via inhalation were acceptable and higher than those of adults, but reverse for carcinogenic risk. Comparatively, the non-carcinogenic and carcinogenic risks of PTMs via ingestion pathway were both higher than those for adults. Although the risks from ingestion were in acceptable range, the total carcinogenic risks for children were more than 10^-4, which would bring carcinogenic risks and should be paid attention to. It was noted that the toxic metal, Co in all size fractions was the most important contributor for noncarcinogenic risks and Cr mostly for carcinogenic risks via inhalation pathway for adults and children in local areas. However, Pb was the most important contributor for noncarcinogenic risk both for adults and children via ingestion pathway relative to Co and Cr for carcinogenic risks through hand-to-mouth ingestion. Those observations demonstrated the important role that the smaller particle fractionations in Pb-contaminated alkaline soil played in both bioaccessibility and the refinement of human health-risk assessments for the inhalation and ingestion pathway.

Effects of soil particle size on metal bioaccessibility and health risk assessment

Oral ingestion is the main exposure pathway through which humans ingest trace metals in the soil, particularly for children. Metals in different soil particle size fractions may vary in terms of concentration and properties. Urban school/kindergarten soil samples were collected from three cities: Lanzhou in northwest China, Wuhan in central China, and Shenzhen in southeast China. Soil samples were classified according to particle size (<63 μm, 63-150 μm, 150-250 μm, and 250-2000 μm) to estimate the effects of soil particle size on the total content and bioaccessibility of metals (Cd, Cr, Cu, Ni, Pb, and Zn). Based on the results, we assessed whether the standard size <150 μm (containing < 63 μm and 63-150 μm), recommended by the Technical Review Workgroup (TRW) of the Environmental Protection Agency (EPA), and <250 μm (containing < 63 μm, 63-150 μm, and 150-250) recommended by the Bioaccessibility Research Group of Europe (BARGE), are suitable where the largest proportion adhering to hands is the finest soil (<63 μm). The results showed that different metals exhibited different relationships between soil particle size and content and between soil particle size and bioaccessibility. Pb and Zn generally exhibited the greatest bioaccessibility in the coarsest particle sizes (250-2000 μm); whereas the highest Ni bioaccessibility occurred in the finest sizes (<63 μm); the bioaccessibility of other metals did not exhibit any obvious relationships with particle size. When assessing health risks using bioaccessible metal content in the recommended soil particle size ranges (<150 μm and <250 μm) and in finer particles (<63 μm), the results for noncarcinogenic risks to children exhibited no obvious difference, while the actual carcinogenic risks may be underestimated with the use of soil particle size ranges < 150 μm and <250 μm. Therefore, when choosing an optimal particle size fraction to evaluate the health risk of oral soil ingestion, we recommend the use of the bioaccessible metal content in <63 μm soil fraction.

Absorption, accumulation and distribution of metals and nutrient elements in poplars planted in land amended with composted sewage sludge: A field trial

Interest in the application of sewage sludge as amendments to grow trees has continued to increase, especially for fast-growing trees such as poplars. In this study, two-year field trial was conducted to determine the effects of compost sewage sludge (CSS) soil application on the distributions of metal and nutrient elements in poplars (Populus × euramericana 'Guariento') and poplar growth. Soil was amended with one of four CSS treatments in both study years: control (2012, 2013: 0 t/ha), SS1 (2012: 7.5 t/ha, 2013: 15 t/ha), SS2 (2012: 15 t/ha, 2013: 30 t/ha), and SS3 (2012: 30 t/ha, 2013: 45 t/ha). During the two-year field trial period, CSS treatments significantly affected leaf K, Mg, Ni, Cr, and Pb contents and root P contents. The element contents in different plant parts responded differently to the different CSS application rates; microelement contents in roots and trace element contents in leaves were significantly affected by the high sludge treatment. The CSS application significantly influenced Ca, Na, Cu, Ni, and Pb accumulation in aerial parts of poplar and the distributions of N, S, Ni, Mg, and P between roots and leaves or stems, and significantly increased the diameter at breast height (DBH) of poplars by 2.4-18.6%. The CSS application of 15 t/ha per year resulted in the largest average increase in DBH of 11.1%; therefore, it could be considered as the most suitable application rate. In summary, CSS application can improve nutrition uptake in various parts of poplars and promote the growth of poplar. Poplar forest amendment is a good CSS disposal strategy.

Eight Elements in Soils from a Typical Light Industrial City, China: Spatial Distribution, Ecological Assessment, and the Source Apportionment

Contamination with the eight elements, Hg, As, Cr, Cu, Ni, Pb, Zn, and Cd, is a serious concern in Zhongshan, which is a typical light industrial city, China. 60 surface soil samples were collected to investigate the concentrations, spatial distribution, human health risk, and sources of these elements in the soils in Zhongshan. The concentrations of the eight elements were analyzed while using ordinary kriging analysis, pollution load index (PLI), potential ecological risk index (RI), human health risk, correlation analysis, and factor analysis. The mean concentrations of the tested elements, excluding Pb and As, were higher than the soil background values in the Pearl River Delta. The spatial distribution of the tested elements revealed a zonal distribution pattern and high values in several areas. The mean PLI and RI indicated slight and moderate risk levels. Health risk assessment demonstrates that both children and adults were more exposed to Cu than to Cr, As, and Cd. However, the associated carcinogenic risk is acceptable. Hg that originated from human activities; As, Cr, Cu, Ni, and Cd originated from industrial activities; and, Pb and Zn originated from transportation activities. Cd was the main pollutant in the study area and it was present at higher concentrations when compared with those of the other elements. Therefore, Zhongshan should encourage enterprises to conduct industrial transformation to control the ecological risk.

Ionic speciation and risks associated with agricultural use of industrial biosolid applied in Inceptisol

The evaluation of the chemical leaching potential from soils amended with biosolid is of extreme importance for environmental safety of agricultural use of these residues. The objective of this study was to evaluate the polluting potential and possible risks associated with the agricultural use of biosolids generated by the polyethylene terephthalate (PET) fiber and resin industry through ionic speciation and analysis of the activity of chemical species present in the leached solution from Inceptisol treated with rates 0, 6, 12, 18, 24, 48, 96, and 144 Mg ha^-1 on dry basis. The experiment was conducted in a lysimeter and the treatments with three replications were distributed at random. Chemical leaching was made by application of CaC1₂ 0.01 mol L^-1 solutions in a volume fourfold higher than the water retention capacity of the soil, divided into five leaching events: 210, 245, 280, 315, and 350 days of incubation. Chemical species concentrations in collected leachates were used for ionic speciation by geochemical software Visual MINTEQA2 version 4.0. Impact factor of chemical species was calculated as the ratio between maximum concentration in the leach solution in the treated soil and control. Dissolved organic carbon had strong influence on Pb⁺² and Cu⁺² leaching, but these elements in free or complexed forms presented low activities in solution. Leaching of NO₃^-, Zn⁺², and Na⁺ represents the main environmental risk of agricultural use of this residue. However, these risks can be minimized if technical criteria and critical limits for the agronomic use of biosolids were observed.

Risk element accumulation in Coleoptera and Hymenoptera (Formicidae) living in an extremely contaminated area-a preliminary study

The risk element accumulation ability of two groups of epigeic species, insects from families Coleoptera and Hymenoptera (namely Formicidae), was determined and related to soil risk element content and bioaccessibility. The study was conducted in the district of Příbram, Czech Republic, which was characterised by extremely high aged pollution in the soils, including risk elements, especially As, Pb, Zn and Cd, due to the former mining and smelting activity. Four sampling sites differing in their pseudo-total risk element contents were selected and composite samples of individuals representing either Coleoptera or Formicidae were sampled at the individual sampling points. The results indicate the ability of Coleoptera and Formicidae organisms to accumulate risk elements, especially at the location with extremely high soil risk element content. In soil containing up to 841 mg As kg^-1, 84.6 mg Cd kg^-1, 4250 mg Pb kg^-1 and 8542 mg Zn kg^-1, contents in insect bodies reached 239 mg As kg^-1 As, 24.2 mg Cd kg^-1, 70.4 mg Pb kg^-1 and 335 mg Zn kg^-1 in beetles and up to 20.9 mg As kg^-1, 29.9 mg Cd kg^-1, 111 mg Pb kg^-1 and 657 mg Zn kg^-1 in ants. Therefore, bioaccumulation factors (BAFs) varied between 0.02 and 0.55. Increasing Cd content in Coleoptera bodies with increasing soil pseudo-total element content was observed only among the investigated elements. However, the results indicate increasing BAF values with decreasing soil element levels, especially for Cd, Pb and Zn, indicating limited uptake of elements by the organisms living in contact with extremely contaminated soil.

Degradation of Triclosan and Carbamazepine in Two Agricultural and Garden Soils with Different Textures Amended with Composted Sewage Sludge

Composted sewage sludge (CSS) has been extensively used in agriculture and landscaping, offering a practical solution for waste disposal. However, some pharmaceutical and personal care products (PPCPs) like triclosan (TCS) and carbamazepine (CBZ) have restricted its land application. In this study, CSS was added to agricultural soil and garden soil at 0%, 5%, 10%, and 25% (w/w soil), and 4 mL of TCS and CBZ stock solution (1000 mg/L in methanol) was spiked into soil amended with CSS of each bottle to arrive at the concentration of 10 mg/kg. Samples were then collected after incubation for 120 days and analyzed for concentrations and half-life (t1/2) of TCS and CBZ, and soil physicochemical properties, together with enzyme activities. The results showed that TCS was degraded completely during the incubation period. In contrast, only about 5.82⁻21.43% CBZ was degraded. CSS amendment inhibited TCS and CBZ degradation and prolonged t1/2 compared to the control, and the t1/2 of TCS and CBZ increased with CSS addition amount in all treatments except for CBZ in the garden soil amended with 10% CSS. Correlation studies showed a significantly positive relationship between t1/2 of TCS and CBZ and total organic carbon (TOC), while a significantly negative relationship between t1/2 of the two PPCPs and pH was observed. Alkaline phosphatase showed a significantly negative relationship with the Ct/C₀ of TCS in garden soil amended with 25% CSS and CBZ in the control. The urease activity was negatively correlated with the Ct/C₀ of TCS in 10% and 25% CSS treatments and CBZ in 10% CSS treatment for garden soil.