Environmental risk assessment (ERA) is a useful methodology to estimate the possible adverse effects to human health due to contaminants exposure. In the case of agricultural scenarios, this method requires knowing the concentrations of contaminants in soil solution and vegetation, among other parameters. This study aimed to develop multicorrelation models to estimate metal extractable from soil as a function of total metal concentration in soil and soil properties in a cattle manure application scenario. It also aimed to estimate metal concentrations in plant by soil–plant uptake factors (UF). All the multicorrelation models obtained were significant, ranging R² values from 0.44 for Cd to 0.92 for Cu. Soil–plant UF were an adequate method for the estimation of metal concentration in plant, since the relationship between the soil–plant UF and the extractable metal concentration from soil was significantly described by a power model, for all the heavy metals.

Concentrations of potentially toxic elements were measured in soils and five contrasting tropical leafy vegetables grown in a replicated field trial at five contaminated urban agriculture sites in Kampala City, Uganda. Soil contamination at each site could be tentatively ascribed to known waste disposal practices. There was considerable variation in metal uptake between vegetable types. Washing leafy vegetables reduced chromium and lead concentrations but exogenous contamination of leaves also depended on vegetable type, with Gynandropsis gynandra L. showing a marked tendency to accumulate Pb and Cr. For the worst case scenario of children consuming unwashed vegetables, some metal ‘hazard quotient’ (HQ) limits (1.0) were violated at four of the five sites studied. For the 25 ‘site-vegetable’ combinations assessed, the HQ for Pb exceeded 1.0 in 36% of cases. A vegetable-specific site screening tool based on soil extraction with 0.01M CaCl₂ and extrapolation to provide HQ values was assessed.

Leguminous trees have a potential for phytoremediation of oil-contaminated areas for its symbiotic association with nitrogen-fixing bacteria and arbuscular mycorrhizal fungi (AMF). This study selects leguminous tree associated with symbiotic microorganisms that have the potential to remediate petroleum-contaminated soil. Seven species of trees were tested: Acacia angustissima, Acacia auriculiformis, Acacia holosericea, Acacia mangium, Mimosa artemisiana, Mimosa caesalpiniifolia, and Samanea saman. They were inoculated with AMF mix and nitrogen-fixing bacteria mix and cultivated over five oil levels in soils, with five replicates. The decreasing of total petroleum hydrocarbons (TPH) values occurred especially with S. saman and its symbiotic microorganisms on highest oil soil contamination. Despite the large growth of A. angustissima and M. caesalpiniifolia on the highest level of oil, these species and its inoculated microorganisms did not reduce the soil TPH. Both plants were hydrocarbon tolerant but not able to remediate the polluted soil. In contrast were significative hydrocarbon decrease with M. artemisiana under high oil concentrations, but plant growth was severely affected. Results suggest that the ability of the plants to decrease the soil concentration of TPH is not directly related to its growth and adaptation to conditions of contamination, but the success of the association between plants and its symbionts that seem to play a critical role on remediation efficiency.

In order to assess the use of magnetic methods to study vertical migration behavior of metal pollutants in natural soils, a controlled experiment was performed near Belle River, Ontario, Canada. The soil at the site consists primarily of clay-rich glacial till overlain by localized alluvium. Twenty PVC tubes (16″ × 8″) were inserted vertically into the ground as test capsules. Magnetite powder (<5 μm) was distributed on the surface of the soil inside ten tubes (10 grams/tube) to simulate anthropogenic contamination, while the other ten were used as controls. While the surficial magnetic susceptibility (MS) remained fairly stable in controls, decreases of 15–60% were observed in contaminated soil tubes. Post-test MS profiles from soil cores in contaminated tubes show that the magnetic signal is strongest at depths between 4 and 6 cm. Magnetic measurements and chemical analysis (using SEM-EDS) on soil layers with enhanced magnetic signal indicate the presence of iron containing particles, likely magnetite. Overall, the results suggest that magnetite powder migrated vertically downwards at a rate of ∼14 cm/year over the four month period, probably as a result of rainwater infiltration. Such magnetic methods and chemical analytical techniques are useful in the investigation of migration of metal pollutants and the potential depth of soil contamination.

During the intensive flood in May–June 2010, the floodplains in Little Poland Vistula Gap, used mostly for agriculture, were waterlogged for a period of over 1 month. The aim of the study was to assess the effect of the flood on the level of contamination of the soils in this region. The analysis included basic physicochemical soil properties, contents of ten metals, and concentrations of 16 polycyclic aromatic hydrocarbons (PAHs). The studies cover two territories on opposite sites of the river Vistula (Wilkow and Janowiec) differing in their areas (70 and 4.6 km2) and time of water logging (30 and 10 days). Forty soil samples were collected from both areas immediately after the flood event from the upper (0–30 cm) soil layer together with four samples from the 30–60-cm depth layer. This was supplemented by eight samples from the flood-deposited sediment layer (thickness, 2 cm). The concentrations of identified metals (As, Ba, Cr, Sn, Zn, Cd, Co, Cu, Ni, Pb) at all the sampling points were below the Polish legal limits for the upper layer of soils for agriculture use. The same regarded the median contents of nine PAHs compounds specified in the Polish regulations. In both areas, the median contents of Σ16 PAHs (0.21–0.35 mg kg−1), Zn (10.3–10.6 mg kg−1), Pb (9.2–10.7 mg kg−1), and Cd (0.03 mg kg−1) were much below the mean concentrations of those contaminants in arable soils on the national and European levels. The results show that this severe flooding episode in “clean” agricultural area had no immediate negative impact on the soils as regards the basic physicochemical properties (organic matter content, acidity, nitrogen content) and did not result in excessive soil contamination.

The assessment of soil pollution with heavy metals has been studied, based on experimental soil and plant analytical heavy metal data obtained by a pot experiment conducted during 2010–2011 in a green house. A completely randomized block design was used, including the following sludge treatments (in tons per hectare): 0, 6, 12, 18, 24, 30, and (30+treated wastewater) in four replications. Lettuce (Lactuca sativa L.) var. longifolia was used as a test plant. Three indices were proposed, i.e., (1) elemental pollution index, (2) heavy metal load, and (3) total concentration factor. They were found to be linearly and statistically significantly related to the pollution load index, which was used as a reference index, and curvilinearly related to lettuce dry matter yield. It was concluded that the above indices could be used for the assessment of soil pollution level.

Assessing multielement adsorption of trace metals on materials having potential to be used as soil amendments is an essential stage for the remediation success, as soil contamination rarely occurs with a single element. This study evaluated mono-/multielement adsorption of Zn, Cu, Cd, and Pb on aluminum (AMB) and iron mining by-products (IMB, used for comparison). Prior to adsorption, these products were characterized by X-ray diffraction, isoelectric point, infrared spectroscopy, scanning electron microscopy, and microwave furnace digestion. Sorption experiments comprised: (1) pH adjustment (5.5, 6.5, and natural suspension pH), (2) mono- and multielement adsorption, and (3) desorption. Rising pH from 5.5 to natural suspension values (9.5) increased monoelement adsorption of Zn, Cu, Cd, and Pb on AMB up to 3.8-, 1.4-, 6.2-, and 1.1-fold, whereas multielement adsorption was increased up to 17.3-, 2.0-, 20.3-, and 1.2-fold, respectively. Zinc and Cd were less adsorbed than Cu and Pb and more affected by competition. Multielement adsorption at 5.5 pH in AMB resulted in smaller adsorption of Zn (up to 4.6-fold), Cu (1.4-fold), Cd (3.3-fold), and Pb (1.1-fold) when compared with monoelement adsorption. The lower the pH, the smaller the adsorption and the higher the desorption. The AMB showed higher capacity to maintain the elements adsorbed than the IMB.

The effect of different humic fractions on polychlorinated biphenyl (PCB) contamination in soils was tested in the field by means of 53 soil samples from a high-altitude grassland plateau in the Italian Alps. Three humic fractions (humin, humic acids, and fulvic acids) were characterized in parallel by quantifying 12 PCB congeners to establish a direct relationship between PCB levels and humic fraction concentrations. Humin (the most hydrophobic fraction) appears to be the most closely correlated with the amount of PCBs in soil (R ²â€‰= 0.83), while fulvic acid shows the lowest correlation (R ²â€‰= 0.49). The idea of preferential sorption of hydrophobic compounds in the humin fraction is discussed, and the humin carbon content (f ₕᵤₘᵢₙC) is proposed as an improved parameter for evaluating the potential for POP accumulation in soils, replacing total organic carbon (f ₒc). Congener studies revealed that penta- and hexa-substituted-CBs show the optimal combination of physicochemical properties for equilibrating with the humin content in soil. Moreover, f ₕᵤₘᵢₙC/f ₒc is conceptually equivalent to the empirical coefficients used in predictive K ₛₐ equations. In our samples, the f ₕᵤₘᵢₙC/f ₒc was 0.55, a value in between the empirical coefficients proposed in the literature. In predictive equations, the use of f ₕᵤₘᵢₙC instead f ₒc avoids the necessity of using an empirical parameter for a ‘generic’ condition by introducing an experimental parameter (f ₕᵤₘᵢₙC) that takes into account local conditions (organic matter composition).

Over a century of metal processing activity has resulted in widespread metal contamination of soils in Sudbury, ON, Canada. To assess the potential for recovery from the large reductions in metal deposition, critical loads were estimated for metals at 415 sites in Sudbury using an ‘effects based’ approach that is based on exceedance of provincial soil guidelines using multiple independent estimates of metal partitioning (Kd) for each metal. Sudbury soils are heavily contaminated with copper (Cu) and nickel (Ni), with 74 % of samples currently exceeding the provincial soil guideline for Cu and 87 % of samples exceeding the guideline for Ni. Both metals are strongly correlated with other metals (zinc (Zn), cadmium (Cd), lead (Pb)), although they rarely exceed provincial guidelines Copper and Ni are also strongly correlated with organic matter but not soil pH. Based on the most recent Cu and Ni deposition estimates (mid-1990s), it is estimated that between 20 % and 51 % of the sites receive deposition in excess of the ‘effects based’ critical load for Cu and between 5 % and 97 % of sites receive atmospheric deposition in excess of the ‘effects based’ critical load for Ni. These results suggest that Cu and Ni concentrations in soil will generally decrease resulting in slightly fewer sites that exceed the provincial soil guideline, but that the timeframe of this response will be very slow, with relatively little change occurring over the next 100 years. Even assuming a best case deposition scenario whereby Cu and Ni deposition were to immediately fall to background levels, the percentage of sites with Cu and Ni levels in excess of the OMOE guideline would still be between 69 % and 72 %, and 56 % and 86 %, respectively, demonstrating that while recovery of the Sudbury soils is possible, greater reductions in metal deposition are needed and even so, it will be a process that takes several centuries.

Tests were conducted to study the influence of non-ionic surfactants Triton X-100 and Tween 80 on the removal of mixed contaminants from a sandy soil using phytoremediation. Cd(II) and Pb(II) were used to form the inorganic contaminant, while used engine oil was selected to form the organic contaminant. The Indian mustard (Brassica juncea) plant was the plant chosen for phytoremediation of the sandy soil that contained the mixed contaminant. Thirty days after the plants were grown in the greenhouse, surfactants were applied to test pots in which the soil had been spiked with 50 mg kg−1 of CdCl2, 500 mg kg−1 of PbCl2 and 500 mg kg−1 of used engine oil. Two control tests were conducted in this study. Planted and unplanted control tests were conducted using soil without surfactants. Following these tests, the tests were completed using the plants and surfactants at different concentrations. Test results showed that Triton X-100 and Tween 80 at concentrations higher than their critical micellar concentration enhanced Cd(II) and Pb(II) accumulation in the plant roots. Further, test data showed that translocation of contaminants to plant shoots occurred for Cd(II) but not for Pb(II). At the same concentrations, Tween 80 was more effective than Triton X-100 in facilitating rhizodegradation of used engine oil. This study demonstrates that simultaneous phytoremediation of Pb(II), Cd(II) and oil can be enhanced by using non-ionic surfactant Tween 80. Leaching test results indicated that the enhanced phytoremediation could remove the mixed contaminants safely from the point of view of limiting groundwater contamination.