L. Madrid

Soil pollution by PAHs in urban soils: a comparison of three European cities

The purpose of this study was to determine the degree of contamination with polycyclic aromatic hydrocarbons (PAHs) in samples of urban soil from three European cities: Glasgow (UK), Torino (Italy) and Ljubljana (Slovenia). Fifteen PAHs (naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]perylene, indeno[1,2,3-c,d]pyrene) were measured in urban soil samples, using harmonised sampling, sample extraction and analyte quantification methods. Although the mean concentration of each PAH in urban soils of each city showed a wide range of values, high levels of contamination were only evident in Glasgow, where the sum of concentrations of 15 PAHs was in the range 1487-51,822 microg kg(-1), cf. ranges in the other two cities were about ten-fold lower (89.5-4488 microg kg(-1)). The three predominant PAHs were phenanthrene, fluoranthene and pyrene, with the sum of these compounds about 40% of the total PAH content. These data, together with some special molecular indices based on ratios of selected PAHs, suggest pyrogenic origins, especially motor vehicle exhausts, to be the major sources of PAHs in urban soils of the three cities. The largest concentrations for PAHs were often found in sites close to the historic quarters of the cities. Overall, the different climatic conditions, the organic carbon contents of soil, and the source apportionment were the dominant factors affecting accumulation of PAHs in soil.

Metal content of surface soils in parks and allotments from three European cities: initial pilot study results

A pilot study of metal content and basic soil properties was undertaken in a number of parks and allotments in the cities of Glasgow, UK, Torino, Italy, and Sevilla, Spain. Between 40 and 60 samples were collected from each city, with soil from two depths. The maximum metal contents (aqua regia) found were 698 mg/kg Cu; 1004 mg/kg Zn; 300 mg/kg Ni; 356 mg/kg Cr and 7051 mg/kg Pb. Variability of metal content showed similar patterns across all cities, with a number of outlier data points. Surface and subsurface samples were comparable within sites. Cu, Zn and Pb levels appeared to contain most variability and extreme data points, while Ni and Cr were more homogeneous. The data support previously published observations of anthropogenic association (Cu, Zn and Pb) and natural sources (Ni and Cr), found in urban environments influenced by diffuse pollution. Within the Glasgow data, differences in the variability of metal content in park and allotment soil are not dramatic, but do reflect the influence of different agronomic activities. The study has provided baseline information for ongoing pan-European urban soil research funded through the EU.

Release of metals from homogeneous soil columns by wastewater from an agricultural industry.

The effect of discharging olive mill wastewater (OMW) in soils on the release of metals previously retained by them is simulated by leaching homogeneous soil columns with a solution of the residue after passing solutions of Cu or Zn through the columns. The effect of other residues, previously added to the soil as composts in field experiments, on the behaviour observed in the laboratory is also discussed. OMW shows a strong power for releasing the metals retained. Previous addition of a compost made from olive mill sludge and plant refuse to the soil causes a significant reduction of the release of retained metal by liquid OMW. Previous addition of concentrated sugarbeet vinasse causes much less significant effects.

Cu(II)-glyphosate system: a study by anodic stripping voltammetry and the influence on Cu adsorption by montmorillonite

The influence of the pesticide glyphosate (GPS) on the adsorption of Cu (II) on montmorillonite has been examined. The complexation of Cu(II) with GPS was studied using anodic stripping voltammetry in differential pulse mode (DPASV). It has been concluded that the complexes present a labile behaviour and GPS shows a low but noticeable degree of heterogeneity, probably due to complexation of Cu bv more than one GPS species. Cu(II) adsorption on montmorillonite is drastically decreased in the presence of GPS, due to several reasons: decrease in free Cu concentration due to formation of Cu-GPS complexes; surface loading of GPS on montmorillonite, obstructing interlamellar Cu2+ adsorption and competitive effect between protons and Cu2+ for interlamellar positions.

Effect of flood with mine wastes on metal extractability of some soils of the Guadiamar river basin (SW Spain)

The availability of metals in soils affected by the accidental flood of mining wastes in the Guadiamar river (SW Spain) is studied at three sites by sequential extraction and by extraction with CaCl2 and EDTA solutions. Significant increases in the available fractions of some potentially toxic metals like Pb and Zn, and in some cases Cu, were found by sequential extraction in the first 5 cm of the soils studied. However, beyond this depth, the pattern was variable along the river. At two of the sites the metals in soluble form did not penetrate further than 5 cm into the soil, while at the site closest to the mineworks, the soluble forms of some potentially toxic metals such as Pb, Zn and, to a lesser extent, Cu, were significantly more abundant at depths >5 cm of the affected soils than those of analogous unaffected soils. The results indicate that the environmental hazard of metal availability for plants penetrating further than 10 cm is not likely to be significant, although it varies along the river. Further studies are needed to assess the long-term environmental damage to the area after removal of the wastes.

Comparison of two methods of sample preparation for determination by atomic absorption spectro‐photometry of heavy metals in soils and sediments

Abstract Two commonly used methods of dissolution of heavy metals in soils and sediments for atomic absorption spectrophotomety (AAS) determination were compared. Dry ashing and subsequent dissolution with 3 N HCl in a block digestor was shown to give a better estimate of the aqua regia‐soluble fraction than wet ash digestion with a mixture of HNO3 and HClO4 acids using reference materials. But both methods extracted significantly less than the certified total contents of most metals. In soils and sediments from SW Spain, the amounts extracted by the block heater method were generally greater than those obtained by wet ash digestion. In agricultural soils, highly significant differences were found between the amounts of Fe, Cu, and Zn extracted by both methods, but the significance decreases if both methods are used on soils or sediments from mining areas where metal contents are likely to be from recent deposits.

Effect of an organic amendment on availability and bio-accessibility of some metals in soils of urban recreational areas.

A composted biosolid from wastewater treatment was added to soils of two public parks of Sevilla, and successive samples were taken during one year. In one of the parks, a second addition of biosolid was carried out after the first year. The soil contents in metals (pseudo-total) and their plant-available and oral bio-accessible fractions were significantly altered when the soils were amended with biosolid. Increase of the bio-accessible metal contents represents a deterioration of the environmental quality of recreational areas, where hand-to-mouth transfer of pollutants to children is likely to occur, although part of the metals added might be leached by rainfall or irrigation. The limits established in several countries for metal contents of soils in recreational areas are often exceeded after application of the biosolid. A careful study of the metal contents of recycled wastes is thus recommended before being used for green area maintenance.

Na/Pb, Na/Cd and Pb/Cd exchange on a low iron Texas bentonite in the presence of competing H+ ion

Abstract The competitive sorption of Pb2+, Cd2+, and H+ ions onto a low iron Texas bentonite (BL) has been studied under conditions where the quantity of Pb2+ and Cd2+ ions was equivalent to the cation exchange capacity (CEC) of the clay and the amount of added acid ranged from 0 to 1 mmol H+ (g clay)−1. Clay concentrations were in the range 25–50 g dm−3 and [M2+] ranged from 0.02 to 0.04 mol dm−3. The adsorption of both Pb2+ and Cd2+ ions onto Na+-BL was reduced as the amount of H+ was increased to values equivalent to the CEC (1 mmol H+ (g clay)−1). Increasing the quantity of Pb2+ to the clay either by increasing the aqueous Pb2+ concentration or reducing the clay content in the suspension had little influence on the shape of the uptake curves for Pb2+ and H+. Cd2+ ions were less able to compete with aqueous H+ ions for exchange sites on Na+-BL than Pb2+ ions. Pb2+ competed more effectively with H+ for the exchange sites on Cd2+-BL than Cd2+ was able to compete with protons for the sites on Pb2+-BL. Protons were less able to compete for exchange sites on both Pb2+- and Cd2+-BL when the aqueous phase contained 1 CEC of Pb2+or Cd2+, respectively.

Solubilization of heavy metals from a river sediment by an olive oil mill effluent at different pH values

The effect of solutions of wastewater from olive mill, called ‘alpechin’, on the solubilization of Ni, Cd, Zn, Cu, Mn, Pb and Fe present in a sediment from Agrio river (Seville, Spain) at pH 3, 4 and 5 is studied. Metal solubilized by alpechin solutions is compared with data from different fractions of metal speciation of the sediment. The data shows that the dominant effect is pH for all metals with the exception of Fe and Mn. Within a given pH, it is shown that the presence of alpechin solutions causes mobilisation of most metals studied at pH 5 except Cd and Zn and this effect is progressively less marked as pH decreases, so that at pH 4 mobilisation is detected for Ni, Cu, Mn and Pb, and at pH 3 only is noticeable for Ni and Mn. The joint effect of pH and of the presence of alpechin is the release of amounts of metals which are comparable to those metal fractions attributed to exchangeable and bound to carbonates.

Complexation parameters of heavy metals by olive mill wastewater determined by a cation exchange resin

Abstract Complexing parameters in aqueous systems containing heavy metals and wastewater from olive‐oil mill (WOM) have been estimated using a cation exchange resin method. The parameters estimated were the maximum complexing ability (MCA), the stability constant (Kc) and a parameter indicating the stoichiometrical characteristics of the complex (a). MCA of WOM for Cu, Zn, Pb and Mn was 0.470, 0.314, 0.068 and 0.300 mmol (g WOM)‐1 respectively, and was related with the ionic radii of the various metal ions. The log Kc values followed the sequence: Cu>Pb>Zn>Mn in agreement with their respective electronegativities. In the case of Cu and Pb, data obtained here was compared with that determined in other work.