Plant Bioavailability Research Articles

Trace metal mobilization by organic soil amendments: insights gained from analyses of solid and solution phase complexation of cadmium, nickel and zinc

The accumulation of Cd in soils worldwide has increased the demand for methods to reduce the metal's plant bioavailability. Organic matter rich soil amendments have been shown to be effective in achieving this. However, it is not known how long these amendments can retain the Cd, and whether dissolved organic matter (DOM) released from them can enhance the metal's mobility in the environment. In this study we sought to test the Cd binding capacity of various organic soil amendments, and evaluate differences in characteristics of the DOM released to see if they can explain the lability of the Cd-DOM complexes. We collected ten organic soil amendments from around New Zealand: five different composts, biosolids from two sources, two types of peat and spent coffee grounds. We characterised the amendments' elemental composition and their ability to bind the Cd. We then selected two composts and two peats for further tests, where we measured the sorption of Ni or Zn by the amendments. We analysed the quality of the extracted DOM from the four amendments using 3D Excitation Emission Matrix analysis, and tested the lability of the metal-DOM complexes using an adapted diffusive gradients in thin-films (DGT) method. We found that composts bound the most Cd and that the emergent Cd-DOM complexes were less labile than those from the peats. Ni-DOM complexes were the least labile. The aromaticity of the extracted DOM appears to be an important factor in determining the lability of Ni complexes, but less so for Zn and Cd.

The role of organic acids in heavy metal tolerance in plants

Organic acid metabolism is of fundamental importance at the cellular and at the whole plant level. In recent years there has been increased attention in the role of organic acids in modulating adaptation to the environment, including organic acids participation in the detoxification of heavy metals. The basis of the phenomenon is the ability of acids such as citrate, malate, oxalate, malonate, aconitate and tartrate to form strong bonds with heavy metal ions through metal chelatation with carboxyl groups carrying the function of donor oxygen in metal-ligands. This review deals with aspects of extracellular and intracellular chelation of heavy metal ions with the involvement of organic acids. We consider the role of metal-induced secretion of malate, citrate and oxalate by roots of various plant species in extracellular complexation of heavy metals and in the reduction of their bioavailability for plants. We also review the possible mechanisms of stimulation of metals uptake by plants under the influence of exogenous application of organic acids in the soil. The efficiency of intracellular chelation of heavy metal ions with the participation of organic acids is considered due to the importance of this strategy in hyperaccumulators and non-hyperaccumulators to improve metal tolerance in plants.

Mercury in rice (Oryza sativa L.) and rice-paddy soils under long-term fertilizer and organic amendment

High levels of mercury (Hg), especially methylmercury (MeHg), in rice is of concern due to its potential of entering food chain and the high toxicity to human. The level and form of Hg in rice could be influenced by fertilizers and other soil amendments. Studies were conducted to evaluate the effect of 24 years application of chemical fertilizers and organic amendments on total Hg (THg) and MeHg and their translocation in soil, plants, and rice grain. All treatments led to significantly higher concentrations of MeHg in grain than those from the untreated control. Of nine treatments tested, chemical fertilizers combining with returning rice straw (NPK1+S) led to highest MeHg concentration in grain and soil; while the nitrogen and potassium (NK) treatment led to significantly higher THg in grain. Concentrations of soil MeHg were significantly correlated with THg in soil (r = 0.59***) and MeHg in grain (r = 0.48***). Calcium superphosphate negatively affected plant bioavailability of soil Hg. MeHg concentration in rice was heavily influenced by soil Hg levels. Phosphorus fertilizer was a main source contributing to soil THg, while returning rice straw to the field contributed significantly to MeHg in soil and rice grain. As a result, caution should be exercised in soil treatment or when utilizing Hg-contaminated soils to produce rice for human consumption. Strategic management of rice straw and phosphorus fertilizer could be effective strategies of lowering soil Hg, which would ultimately lower MeHg in rice and the risk of Hg entering food chain.

Selenium geochemistry in reclaimed phosphate mine soils and its relationship with plant bioavailability

Selenium accumulation in vegetation has resulted in toxicity in livestock grazing on phosphate mine soils in Southeastern Idaho. Plant and soil samples were collected from sites located near phosphate mines. Soil physicochemical properties, Se speciation, and Se distribution from a sequential extraction procedure (SEP) were examined in relation to bioavailability in the Se-hyperaccumulator, western aster (Symphyotrichum ascendens Lindl.). Selenium-hyperaccumulators are plants that can absorb over 1000 mg Se kg−1 DM (Dry Matter). Chemical analyses revealed that western aster contained Se exceeding 6000 mg kg−1 DM. Soil speciation results indicated that selenite (SeO3 2−) was dominant with lower levels of selenate (SeO4 2−) present. This was expanded using an SEP that accounted for six fractions. Regression analyses indicated a strong relationship for western aster Se and the water-soluble and phosphate-extractable SEP fractions combined (R 2 = 0.85). Once carbonate, amorphous Fe-oxide, organic, and residual Se fractions were factored into the analysis, the relationship decreased. A strong relationship between selenate and the water-soluble Se fraction was also observed (R2 = 0.83). Soluble and phosphate-extractable Se were determined to be “bioavailable fractions” for western aster. Thus, simple water extractions can be used for quick assessment of Se bioavailability and provide a means to identify potentially hazardous areas locations.

Combined effect of Cr+6 and chelating agents on growth and Cr bioaccumulation in flood susceptible variety of rice Oryza sativa (L.) cv. Swarna

Flood susceptible variety of Rice (Swarna) were grown in both water logged & water deficit condition. The experimental seedlings were treated with Cr+6 (10mg) and Cr+6 (50mg) both in the presence & in the absence of chelating agents (EDTA-Ethylene Diamine Tetra Acetic Acid, SA-Salicylic Acid, CA-Citric Acid). The results showed that the enhancement of Cr bioavailability in plants occurs by supplementing Cr+6 with chelating agents. This clearly depicts that the role of chelating agents increases the toxic effects of Cr+6 simultaneously increasing the rate of Cr accumulation in rice seedlings.

Evaluation of amendments to reduce arsenic and antimony leaching from co-contaminated soils

Co-contamination of soils with arsenic (As) and antimony (Sb) presents unique challenges for risk management. In this study a sequence of leaching experiments evaluated zero valent iron powder, ferrihydrite, ferric chloride, aluminium and manganese oxides, and kaolinite for As and Sb immobilisation in co-contaminated soils. Iron based amendments were most effective for the reduction of As and Sb in leachate in a column leaching study. Over 48 h zero valent iron powder and ferrihydrite applied at 3% (w/w dry weight) were most efficient, decreasing total As and Sb leachate concentrations by more than 80%. Careful moderation of pH (to > 2.5 but < ∼6) with lime was required for effective co-immobilisation of both metalloids using ferric chloride. In a subsequent batch study with pH optimised for maximum sorption using 2% lime, ferric chloride (3%) added to two co-contaminated soils decreased As and Sb in solution after 7 days by at least 79%. Ferrihydrite (3%) and iron powder (3%) were less effective. Ferrihydrite (3%) was then used in a 12-week larger scale Cynodon dactylon plant experiment that also considered plant bioavailability. Porewater As and Sb decreased by up to 90% but over the 12 week trial period no significant change in shoot or root metalloid concentrations was observed. The study demonstrates that iron-based amendments can be extremely effective for co-immobilisation of As and Sb in contaminated soils, but for large scale application amendment feasibility considerations and site specific pH moderation are essential.

The influence of hydrous ferric oxide, earthworms, and a hypertolerant plant on arsenic and iron bioavailability, fate, and transport in soils.

Historic applications of lead arsenate pesticides and smelting activities have resulted in elevated concentrations of arsenic in Washington State soils. For example, old orchard topsoils in Washington have concentrations reaching upwards of 350mg As/kg soil with an estimated 187,590 acres of arsenic contamination from pesticide application alone. Iron oxides have been indicated as a key factor in modulating the fate and transport of arsenic in the soil environment. We employed a factorial design to investigate the role of a specific iron oxide, hydrous ferric oxide (HFO), and terrestrial organisms on the mobility, bioavailability, and fate of arsenic and iron in locally collected soils. Earthworms in soils amended with both arsenic and HFO had 47.2% lower arsenic tissue concentrations compared to those in soils only amended with arsenic. Similarly, arsenic leachate concentrations and plant tissue concentrations were lower when HFO was present, although this was with a reduced magnitude and was not consistently significant. A lack of significance of HFO in three of the linear models for leachate and plant bioavailability, however, indicates that the role of HFO in arsenic mobility, bioavailability, and fate is more complicated than can be explained by the simple addition or not of HFO. For example, our analyses showed that earthworms decreased pH and increased bioavailability for both arsenic and iron as demonstrated by increases in leachate and plant tissue concentrations. The mechanisms for this could include a biotransformation of earthworm-ingested arsenic combined with an earthworm-induced change in pH. We also found that arsenic amendments increased the mobility and bioavailability of iron, evidenced by increased iron concentrations in earthworms, plants, and leachate. A mechanistic explanation for this change in bioavailability is not readily apparent but does support a need for more work on bioavailability when mixtures are present. From these results, it is clear that a combination of biotic and abiotic factors influences metal/metalloid fate and transport in soils, with earthworms being one of the most important factors in our work. Study designs such as the factorial analysis can help to address the role each factor plays while efficiently generating new hypotheses and areas of inquiry; this approach can also bridge knowledge generated through reductionist and holistic approaches to complex environmental problems.

How Do Modern Pesticide Treatments Influence the Mobility of Old Incurred DDT Contaminations in Agricultural Soils?

Even more than 50 years after the ban of DDT in Germany, farmers are still affected by its persistence in contaminated soils. Depending on the crop cultivated on such soils, this often leads to low-level residues of DDT and its metabolites DDE and DDD ("DDX"), which are perceived as a risk by the food value chain. Pesticide formulations used in modern agriculture commonly contain high levels of surfactants, but so far no open-field studies have evaluated the effects of these treatments on the mobility of lipophilic contaminants, such as DDX. In this field trial, a 1.03 ha section was cultivated with Cucurbita maxima under realistic conditions to monitor the mobility of DDX in low-level contaminated agricultural soils in dependence of common pesticide applications. A typical organic treatment was compared to a conventional protocol. Soil samples were taken before and after each application. Samples from the organic section featured significantly higher extractable DDX contents in soil and water compared to the conventional section. The results show that modern pesticide treatments can have an unforeseen, yet significant influence on the mobilization and, subsequently, on the plant bioavailability of incurred DDX residues depending on the formulation composition.

Key factors related to drinking water treatment residue selection for adsorptive properties tuning via oxygen-limited heat treatment

The beneficial recycling of drinking water treatment residue (DWTR) for environmental remediation has attracted growing attention, and oxygen-limited heat treatment has a high potential to improve DWTR adsorptive properties for better recycling. In this study, physicochemical property variation induced by oxygen-limited heat treatment was evaluated for six DWTR obtained from different drinking water treatment plants in Australia, China, and Ireland. The results showed that the changes in many properties, typically amorphous Al and Fe contents, mesopores, specific surface area (SSA), and total pore volume (TPV) of DWTR after treatment, showed inconsistent trends. The treatment also led to the varied lability of metals and As in DWTR although the human bioaccessibility and plant bioavailability of most metals decreased. Accordingly, oxygen-limited heat treatment may not be applicable for all DWTR improvement. Based on these findings, pre-screening processes to evaluate adsorptive properties and metal and metalloid lability were determined. Oxygen-limited heat treatment was more applicable to DWTR with neutral and weak alkaline properties (pH 7.0–7.8), low humic acid (HA) content (<2.09mgg−1), and high amorphous Fe and HA ratio (>5.93), as well as with relatively high amorphous Al and HA ratio and high humin content.

Higher Molecular Mass Organic Matter Molecules Compete with Orthophosphate for Adsorption to Iron (Oxy)hydroxide.

The competition between orthophosphate and water-extractable organic matter (WEOM) for adsorption to iron (oxy)hydroxide mineral surfaces is an important factor in determining the plant bioavailability of P in soils. Chemical force spectroscopy was used to determine the binding force between orthophosphate and iron (oxy)hydroxide that was coated onto atomic force microscopy (AFM) tips and adsorbed with WEOM. The force measurements were conducted at pH 4.65 and 0.02 M ionic strength which are representative of typical acid soil solutions. The chemical composition of the WEOM was determined by ultrahigh resolution electrospray ionization Fourier transform ion cyclotron mass spectrometry. The results indicate a correlation between aromatic WEOM molecules that are greater than 600 Da and the reduced binding force of orthophosphate to WEOM-adsorbed iron (oxy)hydroxide AFM tips suggesting that the molecular mass of aromatic WEOM molecules plays a critical role in regulating the WEOM-P interactions with surface functional groups of minerals. Based on the results of this study, we show the importance of obtaining a detailed, molecular-scale understanding of soil processes that can help develop better management strategies to reduce waste of limited P resources and adverse environmental impacts. Specifically, soil amendments with greater content of high molecular mass aromatic components may positively affect dissolved P use efficiency in soils by maintaining P in soil solution.

Molasses melanoidin promotes copper uptake for radish sprouts: the potential for an accelerator of phytoextraction.

Phytoextraction has been proposed as an alternative remediation technology for heavy metal contamination, and it is well known that chelators may alter the toxicity of heavy metals and the bioavailability in plants. Our previous work demonstrated that an adsorbent-column chromatography can effectively separate melanoidin-like product (MLP) from sugarcane molasses. The aim of this study was to examine the chelating property of MLP and to evaluate the facilitatory influence on the phytoextraction efficiency of Japanese radish. The result showed that MLP binds to all the metal ions examined and the binding capacity of MLP toward Cu(2+) seems to be the highest among them. The metal detoxification by MLP followed the order of Pb(2+) > Zn(2+) > Ni(2+) > Cu(2+) > Fe(2+) > Cd(2+) > Co(2+). Furthermore, in the phytoextraction experiment using copper sulfate, the application of MLP accelerated the detoxification of copper and the bioavailability in radish sprouts. Thus, these results suggest that MLP possesses the potential for an accelerator of phytoextraction in the copper-contaminated media.

Valorization of a treated soil via amendments: fractionation and oral bioaccessibility of Cu, Ni, Pb, and Zn.

The present study aims to transform a treated soil (TS) into a more desirable resource by modifying physico-chemical properties via amendments while reducing toxic metals' mobility and oral bioaccessibility. A hydrocarbon-contaminated soil submitted to treatment (TS) but still containing elevated concentrations of Cu, Ni, Pb, and Zn has been amended with compost, sand, and Al2(SO4)3 to render it usable for horticulture. Characterization and sequential extraction were performed for TS and four amended mixtures (AM1-4). P and K availability and metal bioaccessibility were investigated in TS and AM2. Amendment improved soil properties for all mixtures and yielded a usable product (AM2 20% TS, 49% compost, 30% sand, 1% Al2(SO4)3) satisfying regulatory requirements except for Pb content. In particular, AM2 had improved organic matter (OM) and cation exchange capacity (CEC), highly increased P and K availability, and reduced total metal concentrations. Furthermore, amendment decreased metal mobile fraction likely to be plant-available (in mgkg(-1), assumed as soluble/exchangeable + carbonates fractions). For AM2, estimated Pb bioavailability decreased from 1.50 × 10(3)mgkg(-1) (TS) to 238mgkg(-1) (52.4% (TS) to 34.2%). Bioaccessible concentrations of Cu, Ni, and Zn (mgkg(-1)) were lower in AM2 than in TS, but there was no significant decrease for Pb. The results suggest that amendment improved soil by modifying its chemistry, resulting in lower metal mobile fraction (in %, for Cu and Zn) and bioaccessibility (in %, for Cu only). Amending soils having residual metal contamination can be an efficient valorization method, indicating potential for reducing treatment cost and environmental burden by rendering disposal/additional treatment unnecessary. Further studies including plant bioavailability are recommended to confirm results.

Clothianidin in agricultural soils and uptake into corn pollen and canola nectar after multiyear seed treatment applications.

Limited data are available on the fate of clothianidin under realistic agricultural production conditions. The present study is the first large‐scale assessment of clothianidin residues in soil and bee‐relevant matrices from corn and canola fields after multiple years of seed‐treatment use. The average soil concentration from 50 Midwest US corn fields with 2 yr to 11 yr of planting clothianidin‐treated seeds was 7.0 ng/g, similar to predicted concentrations from a single planting of Poncho 250‐treated corn seeds (6.3 ng/g). The water‐extractable (i.e., plant‐bioavailable) clothianidin residues in soil were only 10% of total residues. Clothianidin concentrations in soil reached a plateau concentration (amount applied equals amount dissipated) in fields with 4 or more application years. Concentrations in corn pollen from these fields were low (mean: 1.8 ng/g) with no correlation to total years of use or soil concentrations. For canola, soil concentrations from 27 Canadian fields with 2 yr to 4 yr of seed treatment use (mean = 5.7 ng/g) were not correlated with use history, and plant bioavailability was 6% of clothianidin soil residues. Average canola nectar concentrations were 0.6 ng/g and not correlated to use history or soil concentrations. Under typical cropping practices, therefore, clothianidin residues are not accumulating significantly in soil, plant bioavailability of residues in soil is limited, and exposure to pollinators will not increase over time in fields receiving multiple applications of clothianidin. Environ Toxicol Chem 2016;35:311–321. © 2015 The Authors. Published by Wiley Periodicals, Inc. on behalf of SETAC.

Compost addition to polluted soils to ensure fruit and vegetable safety

Pollution affects food safety, environmental quality and human health. ln the case of persistent soil pollution such as chlordecone in the French West Indies, horticultural crops can be so polluted as to exceed maximum residue limits. Generally, there is no remediation solution for these polluted soils. Interactions between organic matter and pesticides are known to help reduce the bioavailability of pesticides in soils. Sequestering pesticides in soils by adding compost could be an alternative way of reducing their diffusion into food chains. We added 5% organic matter to the soil upper layer in horticultural fields and pots. The soil to crop transfer for radish, lettuce and cucumber decreased from 33 to 75% according to the crop and the soil type. We demonstrated that sequestration depended on the soil type and the clay physical properties. In nitisols, chlordecone sequestration was mainly due to chemical interactions with the compost particles whereas in andosols, it was partly due to the physical impact of the added compost (allophane collapse). Increasing soil organic matter content reduces pesticide mobility in the soil and hence its bioavailability for plants. Adding organic amendments to soils is a promising way to reduce the risk of pesticide contamination of food and thus decrease human exposure to potentially harmful chemicals.

Effects of biochar and Arbuscular mycorrhizae on bioavailability of potentially toxic elements in an aged contaminated soil

Biochar pyrolyzed from corn stalks at 300 °C/500 °C and arbuscular mycorrhizae (AMF) were examined independently and in combination as possible treatments for soil remediation contaminated with Cd, Cr, Ni, Cu, Pb, Zn after 35 years following land application of sewage sludge in the 1970s. The results showed that biochar significantly decreased the heavy metal concentrations and their bioavailability for plants, and both biochars had similar such effects. AMF inoculation of corn plants had little effect on heavy metal bioavailability in either control or biochar amended soil, and no interaction between biochar and AMF was observed. Changes in DTPA extractable metals following biochar addition to soil were correlated with metal uptake by plants, whereas pore water metal concentrations were not predictive indicators. This research demonstrates positive benefits from biochar application for contaminated soil remediation, but remain ambiguous with regard to the benefits of simultaneous AMF inoculation on reduction of heavy metal bioavailability.

Biogeochemical processes at soil-root interface

Rhizosphere is a microsite where interactions among roots, microorganisms, soil constituents (minerals and organic matter), and soil solution take place. Biomolecules produced by plants and microorganisms and soil organic substances are involved in many biogeochemical processes at soil-root interface such as: a) weathering of clay minerals and release of Al and Fe, b) formation of nanoprecipitates and organo-mineral complexes, c) sorption/desorption of cations and anions on/from soil colloids and d) bioavailability of nutrients and pollutants. Many exudates form strong complexes with Fe and Al ions, retard or inhibit their hydrolytic reactions and promote the formation of noncrystalline or short-range ordered Al and Fe nanoprecipitates. The so-called iron plaques, present on many wetland plant roots, are Fe(III)-oxyhydroxides (mainly ferrihydrite). These precipitates may interact with biopolymers (proteins, polysaccharides, DNA, RNA and so on), phyllosilicates, soil organic substances as well as microorganisms forming organo-mineral complexes. Root exudates play a vital role on the sorption/desorption of nutrients and pollutants at soil-root interface. The processes, which affect the sorption of cations and anions on sorbents present in the rhizosphere are particularly complex, being sorption of cations quite different from that of anions. Root exudates usually inhibit the sorption of anions, but may promote or inhibit the sorption of cations. They may desorb, at least partially, nutrients and pollutants previously sorbed on soil components, promoting their bioavailability for plants and microorganisms. Finally, some plants release chelating organic ligands able to complex metals (e.g. Al) which become less toxic. Many factors control these processes, for example; pH, nature and concentration of the biomolecules present in the rhizosphere, nature of sorbent and sorbate, reaction time.

Temporal changes in horsebean bioavailability and accumulation after removing extractable oxytetracycline fractions in soils

Extractable fractions of oxytetracycline in soil affect its bioavailability and accumulation in plants.

Accumulation of copper and zinc fractions in vineyard soil in the mid-western region of Santa Catarina, Brazil

The application of fungicides to grapevines can cause the accumulation of Cu and Zn fractions in soil and increase their bioavailability and toxicity for plants. This study evaluated the accumulation and distribution of Cu and Zn fractions in the soil profile of a vineyard. In January 2012, stratified samples were collected from a 95-year-old vineyard and from a forest, which was used as a reference. The soil was dried, ground, and subjected to an analysis of chemical properties and chemical fractionation of Cu and Zn. Cu and Zn accumulated in the most superficial soil layers of the control area and vineyards; greater amounts were found in the soil of vineyards with more than 90 years of Bordeaux mixture application. Most of the Cu and Zn in the control area and vineyard soils were distributed in the residual fraction, with low geochemical mobility; however, they were also found in the most superficial layers of the vineyard soil. There were increases in the contents of soluble Cu, exchangeable Cu, and Cu bond to organic matter of the vineyard soil, especially in the most superficial layer of the soil. Most of the Zn in the vineyard soil was distributed in the residual fraction and bound to minerals, with low mobility but potential toxicity to plants.

Carbonate, organic and clay fractions determine metal bioavailability in periurban calcareous agricultural soils in the Mediterranean area

A set of periurban calcareous agricultural Mediterranean soils, with a natural gradient in the content and composition of organic matter (OM), was spiked with a mixture of Cd, Cu, Pb and Zn at two levels – designated Tt1 and Tt2 – within the limit values proposed by the current European legislation and incubated for ≤12months. We conducted bioassay experiments with romaine and iceberg varieties of lettuce (Lactuca sativa L.). Metal bioavailability patterns were evaluated as a function of soil constituents and extractable metals.Metal contamination produced a decrease in plant biomass (up to 50%) and nutrient imbalance. The redundancy analysis showed that the carbonate, OM and fine mineral fractions account for up to 85% of the variance in metal bioavailability patterns in lettuce plants. Carbonate and fine mineral fractions were negatively related to Cd and Zn bioavailability in plants respectively. Organic matter explained Cu and Pb bioavailability, although patterns varied between plant tissues according to their organic composition. The labile fraction limited metal absorption of Pb by roots at the Tt2 level and Cu at both levels, but Cu and Pb translocation was enhanced at both levels. There were significant correlations between metals in leaves and metals extracted with both neutral salts and complexing agents. The high rate of metal translocation and the considerable influence of soil properties may indicate that the limiting values of metals in soils proposed by the current European legislation should be revised in the case of multi-component systems, and/or be established according to the soil characteristics.

The Effect of Thiosulphate on Arsenic Bioavailability in a Multi Contaminated Soil. A Novel Contribution to Phytoextraction

In this study it was evaluated on a laboratory scale (microcosm), the possibility of using ammonium thiosulphate in assisted phytoextraction for the simultaneous removal of mercury and arsenic from multi- contaminated industrial soil. The species selected were Brassica juncea and Lupinus albus the addition of thiosulfate to the soil greatly promoted the uptake and translocation of both contaminants in the aerial parts of the plants. Mercury concentration in the aerial parts reached in B. juncea 120 mg/kg approximately 40 times the value of the control). The concentration of arsenic also increased significantly in the shoots of B. juncea (14.3 mg/kg), where the value in the control was negligible. Similar trends were obtained for L. albus The results confirmed the known positive effects of thiosulphate in increasing mercury bioavailability for plants, moreover they showed the ability of thiosulphate to mobilize arsenic and significantly to promote its uptake by plants. The increase of arsenic bioavailability, promoted by thiosulfate addition, could be attributed to the competition between arsenate and sulphate ions for the same active sites in the soil surfaces, with the release of arsenic in the soil solution. The use of thiosulfate appears to have great potential since it is a common fertilizer used to promote plant growth and is able to increase the uptake by plants of mercury and arsenic. The simultaneous increase of both contaminants uptake by plants, using a single additive, will provide new insights into the phytoextraction technology in terms of cost and time reduction.