Incorporation of metal bioavailability into regulatory frameworks—metal exposure in water and sediment

Background, aim, and scope  

The cause for this position paper is the impression that risk assessors consider primarily the concentration of free metal ions dissolved in solution controlling metal bioavailability in aquatic systems. Aiming at a more realistic risk assessment of metals, bioavailability has to be discussed under the scope of main uptake routes of metals to organisms.     

Ants and heavy metal pollution – A review

Ants due to their nesting habits are ideal for studying temporal fluctuations in trace metal accumulation, changes in morphological traits, as well as for assessing evolutionary processes and monitoring environmental impact of metals derived from human activities. Although metal pollution may affect basic ecological traits such as colony size and survival, ants can be considered relatively resistant to metal pollution at least partly due to relatively high metal regulation efficiency. At both polluted and unpolluted areas the body metal levels in ants vary considerably between species. This observation and other experimental data suggest differences in metal regulation physiology, however the physiological basis of these differences remains unknown. It was shown that metal pollution may suppress the immune defense systems, which in turn could theoretically lead to a higher risk of infections. Biodiversity studies are limited, however the evidence for a clear negative influence of metal pollution on ant species diversity and abundance was not yet provided. Since many aspects of ant ecotoxicology remain unclear, the questions for possible future research are suggested.     

Heavy metal accumulation in plants on Mn Mine tailings

The profile distribution of β-gulcosidase activity in twelve typical paddy soil profiles with high productivity in the Taihu Lake region of China were investigated. Activities of β-gulcosidase in the plow layers were in the range of 52.68- 137.02μg PNP g^-1 soil h^-1 with a mean of 89.22μg PNP g^-1 soil h^-1. However, most plow layers ranged from 70 to 110 μg PNP g^-1 soil h^-1. The profile distribution of β-gulcosidase activity in the 12 soil profiles decreased rapidly with soil depth, with activity at the 60 cm depth only about 10% of that in the surface layers （0-15 cm or 0-20 cm）. In these soil profiles, β-gulcosidase activity was significantly positively correlated with soll organic carbon and arylsulphatase activity. Meanwhile, a significantly negative correlation was shown between β-gulcosidase activity and soil pH.     

Methods for remediation of metal‐contaminated soils: Preliminary results

Abstract

Contamination of soils by heavy metals is one of the environmental problems that the scientific community faces today. Such soils are difficult to treat because the heavy metals cannot be destroyed. Moreover, they are usually bonded with other contaminants, in particular organic ones. The presence of these organic pollutants can make the removal of metals from soils substantially more complicated. One way of coping with the problem which has been studied in recent years is the use of fixing agents which make the heavy metals unavailable to the plants, or prevent their leaching towards the groundwater. Inorganic fixing agents in particular have been tested and found to be suitable, but some organic ones can also be used, at least as temporary fixing materials. This paper gives preliminary results on remediation techniques using compost and Trichoderma viride Pers.: Fr. as heavy metal fixing agents.     

Heavy‐metal toxicity in plants 1. A crisis in embryo

Abstract

Heavy metals are often added indiscriminantly to soils in pesticides, fertilizers, manures, sewage sludges, and mine wastes, causing an imbalance in nutrient elements in soils. Heavy‐metal toxicity causes plant stress in various degrees dependent on the tolerance of the plant to a specific heavy metal. The objectives of this study were (i) to show that plant species and soils respond differently to heavy metals and (ii) to show the necessity for proper quantity and balance of heavy metals in soils for plant growth.

Three Fe‐inefficient and three Fe‐efficient selections of soybean, corn, and tomato were grown on two alkaline soils with Cu and Zn ranging from 14 to 340 and Mn from 20 to 480 kg/ha. Heavy‐metal toxicity caused Fe deficiency to develop in these plants. The Fe‐inefficient T3238fer tomato and ys₁/ys₁ corn developed Fe deficiency on all treatments and both soils. T3238FER tomato (Fe‐efficient) did not develop heavy metal toxicity symptoms on any treatment or soil. The soybean varieties and WF9 corn were intermediate in their response.

The unpredictable response of both the soil and the plant to heavy metals make general recommendations difficult. In order to maintain highly productive soils, we need to know what we are adding to soils and the consequences. Without some control, the continued addition of heavy metals to soils is a crisis in embryo.     

Effect of controlled-release urea on heavy metal mobility in a multimetal-contaminated soil

Controlled-release N fertilizers can affect the availability of heavy metals in the contaminated paddy soil.A soil incubation experiment was conducted to investigate the effects of prilled urea(PU),S-coated urea(SCU),and polymer-coated urea(PCU)on the solubility and availability of heavy metals Cd,Pb,Cu,and Zn in a multimetal-contaminated soil.The results showed that the application of different coated urea significantly affected the solubility and availability of heavy metals.At 5 d of incubation,the application of PU,SCU,and PCU had significantly decreased the concentrations of water-soluble and available Cd,Pb,Cu,and Zn,when compared with the control.At 60 d of incubation,the depletory effects of PU on water-soluble and available heavy metals had reduced,and the initial decrease in the concentrations of water-soluble Cd,Pb,Cu,and Zn caused by SCU had changed to an increase.The concentrations of water-soluble Pb,Cu,and Zn in the SCU-treated soil were higher than those in the control.Application with PCU led to a higher water-soluble Cu than that in the control,while the available Cd,Pb,and Zn were lower than those in the control.The effect of different coated urea was much stronger on the water solubility of the heavy metals than on their availability.The effects of controlled-release urea on the transformation of heavy metals resulted in changes in the concentrations of NH4^+,water-soluble SO4^2-,and soil p H.The results further suggested that PCU could be used in dry farming operations in multimetal-contaminated acid soils.     

Natural and induced heavy‐metal accumulation by Arrhenatherum elatius: Implications for phytoremediation

Abstract

The uptake of cobalt, copper, lead, and nickel by the perennial metal‐tolerant grass Arrhenatherum elatius was studied by growing the plants in two different substrates. These were a cobalt/copper/nickel ore (Experiment A) and base‐metal tailings rich in lead (Experiment B). The enhancement of metal uptake by the plants following addition of EDTA was investigated in both experiments. In Experiment A, metal concentrations in dry plant matter were about equal to the acid‐extractable (1 M hydrochloric acid) fractions in the supporting soils after addition of 4 g kg^‐1 EDTA. In Experiment B, the base‐metal tailings contained 11,500 mg kg^‐1 (1.15%) lead. The EDTA addition induced 2.5% lead (dry matter) in the grass. This was reduced to ca. 1.0% upon addition of lime. The results indicate that A. elatius may have some potential in phytoremediation operations if EDTA is added to the substrate.     

The effect of waste water treatment on river metal concentrations: removal or enrichment?

Purpose

Discharge of untreated domestic and industrial waste in many European rivers resulted in low oxygen concentrations and contamination with trace metals, often concentrated in sediments. Under these anoxic conditions, the formation of insoluble metal sulfides is known to reduce metal availability. Nowadays, implementation of waste water treatment plants results in increasing surface water oxygen concentrations. Under these conditions, sediments can be turned from a trace metal sink into a trace metal source.

Materials and methods

In an ex situ experiment with metal contaminated sediment, we investigated the effect of surface water aeration on sediment metal sulfide (acid volatile sulfides (AVS)) concentrations and sediment metal release to the surface water. These results were compared with long-term field data, where surface water oxygen and metal concentrations, before and after the implementation of a waste water treatment plant, were compared.

Results and discussion

Aeration of surface water in the experimental setup resulted in a decrease of sediment AVS concentrations due to sulfide oxidation. Metals, known to precipitate with these sulfides, became more mobile and increasing dissolved metal (arsenic (As), cadmium (Cd), copper (Cu)) concentrations in the surface water were observed. Contrary to As, Cd, or Cu, manganese (Mn) surface water concentrations decreased in the aerated treatment. Mn ions will precipitate and accumulate in the sediment as Mn oxides under the oxic conditions. Field data, however, demonstrated a decrease of all total metal surface water concentrations with increasing oxygen concentrations following the implementation of the waste water treatment plant.

Conclusions

The gradual decrease in surface water metal concentrations in the river before the treatment started and the removal of metals in the waste water treatment process could not be countered by an increase in metal flux from the sediment as observed in the experiment.     

Shannon–Weaver index as an integrated indicator of metal differentiation in soil and plant samples

The degree of contrast (differentiation) in the distribution of metals in background and contaminated soils is one of the most important geochemical indicators. The Shannon–Weaver index (H) can be a suitable criterion for the distribution of metals in soil and plant samples. A procedure for calculating the Shannon–Weaver index is described. An index scale of five gradations, from no differentiation (H_rel = 1.0–0.9) to very high differentiation (H_rel = 0.3–0.1), is proposed. The background soils in different regions of Russia have low or even no differentiation of metals. Aerial pollution of soils with heavy metals appreciably increases the degree of metal differentiation, especially near the source of pollution. The parameter value decreases with increasing distance from the pollution source, probably due to the mechanical dilution of dust in the large soil volume.     

The effect of sewage‐sludge on the heavy metal content of soils and plant tissue

Abstract

Domestic sewage sludge applied to farm fields at a rate of 44.9 kg/ha in a mixture with lime and sawdust was found to increase the soil levels of cadmium, chromium, copper, lead, mercury, nickel and zinc. The average levels in sludge treated soil were: 0.11, 0.56, 3.59, 2.72, 0.068, 1.49 and 2.57 ppm, respectively. The increases were small and the overall loading factors were well below recommended maximums. The uptake of these heavy metals by grass and legume plants was variable with cadmium, copper and zinc levels being higher in those plants growing in the sludge treated soils but only copper was significantly higher. The heavy metal contents found were all within the levels normally found in grass and legume plants. The higher mean concentration in plants growing on the sludge treated soils were cadmium 0.495; chromium 1.22; copper 12.3; lead 1.54; mercury 0.022; nickel 4.08 and zinc 28.4 ppm.     

Residual heavy metal concentrations in sludge‐amended coastal plain soils ‐ I. Comparison of extractants

Abstract

The purposes for this research were: to examine the long‐term residual effects of farmland applications of municipal sludges from four treatment technologies on the total and extractable Zn, Cu, Mn, Fe, Pb, Ni and Cd concentrations in Coastal Plain soils; to investigate the effects of sludge sources and rates on the effectiveness of soil extractants to remove the various metals; and to determine correlation coefficients for soil extractable versus plant accumulation in tobacco. The extractants evaluated were Mehlich 1 and 3, and DTPA‐pH 7.3. Composite Ap horizon soil samples and tobacco leaf samples were obtained in 1984 from research plots at two sites in Maryland that were established in 1972 and 1976, respectively, using sludge materials from three wastewater treatment facilities in the Washington, D.C. metropolitan region. Similar application rates were used at both sites.

A wide range in soil pH values was found among treatments at each site. Significant (p ≤ 0.05) increases were observed in total Zn, Cu, Fe, Pb, Ni, and Cd for all sludge sources with increased rates; however, values for total soil Mn exhibited high variability in all cases. The rankings among the extractants varied for some elements depending on the sludge sources. For Zn, the rankings were Mehlich 1 > Mechlich 3 > DTPA‐pH 7.3 across all sources and rates. For Cu, Mehlich 3 > Mehlich 1 > DTPA‐pH 7.3 was found for soils amended with Blue Plains digested (BPD) and Piscataway limeddigested (PLD) sludges but Mehlich 1 ≥ DTPA pH 7.3 > Mehlich 3 for Blue Plains limed compost (BPLC) and Annapolis Fe and heat treated (AFH) sludges. Concerning extractable Mn, Mehlich Mehlich 1 > Mechlich 3 > DTPH pH 7.3 was the order for BPLC and AFH sludges but Mehlich 3 > Mehlich 1 > DTPA‐pH 7.3 was observed for BPD and PLD sludges. The rankings among extractants for Fe (Mehlich 3 > Mehlich 1 > DTPA‐pH7.3), Ni (Mehlich 3 ≥ Mehlich 1 > DTPA‐pH 7.3), Pb (Mehlich 3 > DTPA‐pH 7.3 > Mehlich 1) and Cd (Mehlich 1 > Mehlich 3 > DPTA‐pH7.3) were somewhat similar across all sludge sources. Significant correlation coefficients were obtained for all three extractants for soil extractable vs. plant Zn, Cu, Ni, and Cd at both sites; however, Mehlich 3 was not significant for Mn. Also, neither of the extractants produced significant coefficients for Fe and Pb.     

Physico – biochemical properties of tomato (Solanum lycopersicum) grown in heavy – metal contaminated soil

The present study was undertaken to investigate the effect of soil contamination with heavy metals on physico-biochemical properties of tomato fruit. The deleterious effect of soil contamination on the quality and quantity of tomato plant yield was determined. Harvested tomato fruit characteristics including fruit length, diameter, volume and fresh and dry weights, total soluble solids, titratable acidity, lycopene and carbohydrates contents were measured in tomato fruits cultivated in soil contaminated with industrial effluents. In addition, some secondary metabolites (total phenols and flavonoids), micro- and macronutrients were also detected. Residual heavy metals (Cd, Co, Ni and Pb) were examined in the harvested fruits. The obtained results were compared with those of tomato fruits cultivated in non-contaminated soil. Results demonstrate that soil contamination with heavy metals have a negative effect on tomato fruits characteristics, titratable acidity, total soluble solids, lycopene, ascorbic acid, micro-elements and carbohydrates content. Moreover, fruits originated from plants grown in contaminated soil possess high phenols and flavonoids contents and higher heavy metals content compared to control fruits. It is recommended that fruits cultivated in that area not to be eaten by large quantities, to avoid excessive accumulation of heavy metals in the human body.

Abbreviations: (AsA): Ascorbic acid; (DTPA): diethylenetriamine penta acetic acid; (TA): Titratable acidity; (TSS): Total soluble solids     

Could the rhizoplane biofilm of wetland plants lead to rhizospheric heavy metal precipitation and iron-sulfur cycle termination?

Journal of Soils and Sediments - Iron plaque (IP) formation via radial oxygen loss (ROL) of wetland plant has been predominantly recognized as the reason for heavy metal sequestration in the...     

Application of soil amendments to contaminated soils for heavy metal immobilization and improved soil quality—a critical review

ABSTRACT

Today, soil metal pollution has become a significant environmental issue of great public concern. This is because soil is both a major sink for heavy metal(loid)s (HMs) released into the environment, by both pedogenic and anthropogenic activities; and also a major source of food chain contamination mainly through plant uptake and animal transfer. In addition, HM contamination of soil leads to negative impacts on soil characteristics and function by disturbing both soil biological and physiochemical properties (e.g. extreme soil pH, poor soil structure and soil fertility and lack of soil microbial activity). This eventually leads to decreased crop production. Various soil remediation techniques have been successfully employed to reduce the risks associated with HMs efflux into soil. Among these, the use of low-cost and environmentally safe inorganic and organic amendments for the in-situ immobilization of HMs has become increasingly popular. Immobilization agents have successfully reduced the availability of metal ions through a variety of adsorption, complexation, precipitation, and redox reactions. Soil amendments can also be a source of nutrients and thus can also act as a soil conditioner, improving the soil’s physiochemical properties and fertility, resulting in enhanced plant establishment in metal contaminated soils. This article critically reviews the use of immobilizing agents in HM contaminated agricultural and mining soils paying particular attention to metal immobilization chemistry and the effects of soil amendments on common soil quality parameters.     

Heavy metal and PCB spatial distribution pattern in sediments within an urban catchment—contribution of historical pollution sources

Purpose

This work analyzes polychlorinated biphenyl (PCB) and heavy metal contamination in fluvial sediments and soils in an urban catchment, according to the geo-accumulation index and to soil and sediment quality guidelines. The catchment is located in Coimbra, Portugal, being affected by frequent flooding, and its main stream is a tributary to one of the major rivers in Portugal (Mondego). Given the presence of industrial activities over time, some inputs of pollutants are expected, but so far, the legacy of historic pollution in this catchment has not yet been investigated.

Materials and methods

Twenty-five samples were collected from nine sampling sites at the depths of 0–20, 20–40 and 40–60 cm (to provide a historic perspective) along longitudinal profiles (streamlines) and in soils downstream of pollution sources. These samples were analyzed for six heavy metals (Cu, Cr, Pb, Cd, Zn, Ni), organic carbon, pH and ten PCBs (IUPAC numbers 28, 30, 52, 101, 138, 153, 166, 180, 204, 209).

Results and discussion

Total PCB concentrations ranged 0.47–5.3 ng g^?1 dry weight (dw), and levels increase from the bottom to the top layers, suggesting an increased input over the last 100 years. PCB congener distribution shows the dominance of hexachlorobiphenyls, especially PCB138, suggesting the existence of local sources. PCB levels did not exceed sediment quality levels, placing sediments/soil under class 1 (not contaminated) or class 2 (trace contamination) with respect to PCB. All six metals exceeded the lowest effect level for sediment quality criteria, and three (Cd, Pb and Zn) largely exceeded the clean levels for dredged materials, placing sediments in class 5 (heavily contaminated). Sampling site S1 presented the highest concentrations of Zn, Pb and Cd, and historic vehicle traffic was identified as the most likely source, given the vertical and horizontal profiles.

Conclusions

High levels of Pb, Cd and Zn were found in fluvial sediments at some locations of the Loreto catchment, likely from historic traffic sources. This urban area is frequently affected by flooding events and is currently being subject to urban redevelopment. During these events/actions, historic pollutants in the sediments might surface and be redistributed, impacting the downstream ecosystem of the major Mondego River or increasing the risk of exposure of the urban population.

     

Remediation of heavy metal(loid)s contaminated sediments—in situ iron treatment and subsequent magnetic extraction

Purpose

Surface sediments contaminated with high levels of multiple heavy metal(loid) species are very common environmental problems. Especially, the labile and bioaccessible fractions of heavy metal(loid)s in the sediments are posing serious risks to the biota and the overlaying water quality. This study aimed at developing a potential method to manage the activity of the labile fractions of heavy metal(loid)s in surface sediments.

Materials and methods

This study assessed the feasibility of adding iron powder, a low-cost industrial by-product, to sediments containing high levels of Pb, As, and Cd to adsorb labile fractions of heavy metal(loid)s onto the sorbent surfaces and to retrieve the heavy metal(loid) laden powders by applying external magnetic field. In addition, the redistribution of Pb, Cd, and As in different sediment fractions, the dissolved fraction and the sorbent-adsorbed fraction, was also investigated and characterized.

Results and discussion

The results indicate that the bioactive labile fractions (exchangeable and carbonate-bound fractions) of heavy metal(loid)s are prone to concentrating onto iron powders and can be selectively removed from the sediments by magnetic retrieval. In addition, iron addition induces conversion of labile fractions of heavy metal(loid)s into more stabilized fractions.

Conclusions

Overall, the process can effectively minimize the activity of labile fractions of heavy metal(loid)s in surface sediments.

     

Changes in organic matter and enzymatic activity of an agricultural soil amended with metal‐contaminated sewage sludge compost

Abstract

The effect of organic amendment with sewage sludge composts of varying heavy metal content on the organic matter content and enzymatic activity of an agricultural soil supporting barley (Hordeum vulgare L.) or lettuce (Lactuca sativa L.) crops was studied. The organic amendments did not improved lettuce growth, the contaminated composts having a negative effect on yield. However, all organic amendments improved barley straw yields although they did not affect grain yields. The addition of the organic materials increased the total carbohydrate content of the soil although this content decreased with cultivation. There was a clearly observed effect of crop type and the degree of heavy metal contamination of the amendment on the most labile carbon (C) fractions (water‐soluble C, carbohydrates, and polyphenolics). In general, soil enzymatic activities were stimulated by addition of sewage sludge compost with low heavy metal content. The compost containing high level of cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn) inhibited protease‐BAA activity with respect to the other composts. After cultivation, urease activity increased in soil amended with the high dose of composts, regardless their degree of metallic contamination. Both crop type and metallic contamination contained in the organic materials added influenced phosphatase and ß‐glucosidase activity.     

High phosphorous levels on zinc and other heavy metal concentrations in Hawkeye and PI54619–5–1 soybeans

Abstract

Two soybean varieties were grown at different P levels to test tolerance to high levels of P. When Hawkeye and PI54619–5–1 soybeans, Glycine max (L.) Merr. Bragg, were grown in solution culture with NH₄ H₂ PO₄ increasing from 10^‐4 M to 3 × 10^‐2 M, yields of Hawkeye were decreased more by the highest P levels than were those of PI54619–5–1. The high P also resulted in larger concentrations of Zn, Cu, and other heavy metals in Hawkeye man in PI54619–5–1. Phosphorous concentrations were generally higher for Hawkeye than for the PI54619–5–1 soybeans. PI54619–5–1 leaves contained less of most metals than the Hawkeye.     

Chemical fractions of copper and zinc in organic‐rich particles from aqueous extracts of a metal‐contaminated granite soil

Abstract

Chemical fractions of copper (Cu) and zinc (Zn) in the organic‐rich particles collected from filtered aqueous extracts (<20 μm) of an acid soil were determined. A sequential extraction procedure was used to partition the particulate Cu and Zn into four operationally defined chemical fractions: adsorbed (ADS), iron (Fe) and manganese (Mn) oxides bound (FeMnOX), organic matter bound (OM) and residual (RESD). Total extractable concentrations of Cu and Zn in the fine particles were higher than their total concentrations in the original bulk soil. The concentration of particulate Cu was usually much higher than that of particulate Zn. Addition of lime stabilized sewage sludge cake and/or inorganic metal salts markedly increased the concentrations of particulate Cu and Zn in aqueous extracts, especially from limed soil. The proportional distributions of particulate Cu and Zn were quite similar. The two particulate metals were present predominantly in the ADS and FeMnOX fractions, with less (about 20%) in the OM and RESD fractions. Some of the ADS metal fraction was associated with dissolved organic substances. The concentrations of particulate Cu and Zn in the various extractable fractions were significantly affected by the application of lime, lime stabilized sewage sludge cake, or inorganic metal salts.