Amparo Cortés

Organic matter fractions controlling the sorption of atrazine in sandy soils

Abstract The soil-water distribution (Kd) of atrazine has been studied in 24 soil profiles, comprising 109 soil horizons derived from granodioritic materials; Kd ranged from 0.01 L/kg to 64 L/kg with a mean value of (2.4 ± 7.3) L/kg. The concentrations of organic carbon, cation exchange capacity, clay, and oxides of iron, aluminum, and manganese were determined. In a multiple linear regression analysis Kd was strongly correlated with the organic carbon content (foc) and weakly correlated with aluminum oxides. No other soil components were correlated with Kd. The organic carbon soil sorption coefficient (Koc) was estimated to be 216 ± 9 L/kg (95% confidence limits) from a linear plot of Kd versus the foc. In a logarithmic correlation between Kd and foc the non-linearity constant proved statistically significant from unity: logKd=(1.81 ± 0.20) + (0.75 ± 0.07) x logfoc which indicates that not only the concentration, but also the composition of the organic matter play important roles in soil sorption of atrazine. In 48 of the 109 soil horizons which contained more than 0.1% of organic carbon, the organic matter was fractionated into humic acids, fulvic acids, humin and free organic matter. A multiple linear regression analysis between Kd and the various organic matter fractions revealed that humic acid (Ha) explained 71% of the variance compared to 26% for humin plus free organic matter (Hum + Fom). In addition, 3% of the variance was explained by manganese oxide: Kd= (167± 11) x Ha-(0.74 ± 0.09) x (Hum + Fom) + (21± 16) x MnO- (1.6± 1.0) Previously published equations for predictions of Koc of a compound from its water solubility and its octanol-water partition coefficient (Kow) were evaluated. Kow proved to be the best predictor for atrazine.

Soil sorption of co‐planar and non‐planar PCBs

Soil sorption of co‐planar and non‐planar PCBs was studied. Dystric Gleysols sampled in a forested area near Lake Maggiore (Italy) were used. The three most toxic congeners, non‐ortho‐substituted PCB 77, PCB 126 and PCB 169 were compared with the moderately toxic mono‐ortho‐substituted PCB 118 and PCB 122 and the lesser toxic di‐ortho‐substituted PCB 52, PCB 101, PCB 138, PCB 153 and PCB 180. Soil sorption of co‐planar PCBs was stronger than of non‐planar PCBs with the same degree of chlorination. Soil sorption of PCBs is favoured by high total organic carbon, high total aluminium and iron oxides and increasing fine particles of soil.

ASSESSING CHANGES IN CD PHYTOAVAILABILITY TO TOMATO IN AMENDED CALCAREOUS SOILS

A plot study was conducted to assess changes in Cd phytoavailability to a tomato cultivar in an agricultural soil in Southeastern Spain amended in two different ways (A and B), under controlled conditions. The experimental soil corresponded to a fine-loamy carbonatic thermic Calcidic Haploxeroll (Soil Survey Staff, Keys to Soil Taxonomy, eighth ed., USDA, Washington, 1998). (A) Soil was amended with a single application of sewage sludge from a municipal source that had a total Cd concentration of 0.5 mg kg(-1) at a rate that represented a final average concentration in the mixture of soil and sludge of less than 50 microg Cd kg(-1). (B) The amendment consisted of the addition of a mineral fertiliser with the same amount of NPK as in the sewage sludge application. The final levels of Cd were supposed to be negligible. A plot series without amendments was also performed (C). DTPA plus triethanolamine, and ammonium acetate extractable fractions in soils were analysed for all the plots. The time-dependent Cd accumulation in different parts of the tomato plants was studied by means of a Cd salt treatment. For each block (A-C) four levels of Cd (0, 3, 30, and 100 mg kg(-1)) were added as CdCl2. There was a significant increase in plant Cd after the initial cropping. Tomato stems, leaves and fruits were analysed separately for Cd determination. Differential Cd distribution and accumulation in tomato parts was detected.

Spatial distribution of copper and pH in soils affected by intensive industrial activities in Puchuncaví and Quintero, central Chile

The soils of Puchuncavi and Quintero, in the coastal area of central Chile, have been exposed to atmospheric deposition of sulfur dioxide (SO 2 ) and metal-rich particles from the Ventanas Industrial Complex. The objective of this study was to determine, using geostatistical tools, the spatial distribution of copper and pH in these soils. Using Universal Kriging tool for geostatistical interpolation, we generated maps of continuous distribution of Cu and pH in the soils. The distribution of these variables was related to the distance from the industrial complex and to the direction of the winds. The concentrations of Cu and acidity were higher in the surroundings to the industrial complex and in the direction of the dominant winds. Although the distributions of both variables were similar, there was no correlation between the distribution of Cu and pH, which could be due to the distinct aerial dispersion dynamics of the compounds, which causes a divergence in their deposition on the soil. Specifically, this could be due to the fact that SO 2 is smaller than the particulate matter that contains copper, so that it is capable of being dispersed over greater distances without being deposited on the soil.

Effect of compost and biodegradable chelate addition on phytoextraction of copper by Oenothera picensis grown in Cu-contaminated acid soils.

Oenothera picensis plants (Fragrant Evening Primrose) grow in the acid soils contaminated by Cu smelting in the coastal region of central Chile. We evaluated the effects of compost, at application rate of 5 kg m(-2), and biodegradable chelate MGDA (methylglycinediacetic acid), at application rate of 6 mmol plant(-1), on Cu phytoextraction by O. picensis, in field plots. No significant differences were found between treatments regarding aboveground biomass, shoot Cu concentrations and Cu phytoextraction of O. picensis. This lack of effects of the treatments was provoked by the large variability of soil properties, prior to applying of the treatments. The shoot Cu concentration in O. picensis positively and significantly correlated to exchangeable Cu concentration in the soil. Likewise, the aboveground biomass of O. picensis positively and significantly correlated to soil organic matter content. The Cu phytoextraction by O. picensis, in turn, positively and significantly correlated to both variables, i.e. exchangeable Cu concentration and organic matter content. The average Cu phytoextraction was 1.1 mg plant(-1), which is equivalent to 90 g ha(-1) at planting rate of 8 plants m(-2). In the chelate treatment, Cu phytoextraction was 2.6±2.1 mg plant(-1), which is equivalent to 212±171 g ha(-1) at planting rate of 8 plants m(-2).

Biodegradable chelate enhances the phytoextraction of copper by Oenothera picensis grown in copper-contaminated acid soils

Oenothera picensis plants (Fragrant Evening Primrose) grow in the acid soils contaminated by copper smelting in the coastal region of central Chile. We evaluated the effects of the biodegradable chelate MGDA (methylglycinediacetic acid) on copper extraction by O. picensis and on leaching of copper through the soil profile, using an ex situ experiment with soil columns of varying heights. MGDA was applied in four rates: 0 (control), 2, 6 and 10 mmol plant(-1). MGDA application significantly increased biomass production and foliar concentration, permitting an effective increase in copper extraction, from 0.09 mg plant(-1) in the control, to 1.3mg plant(-1) in the 6 and 10 mmol plant(-1) treatments. With 10 mmol plant(-1) rate of MGDA, the copper concentration in the leachate from the 30 cm columns was 20 times higher than in the control. For the 60 cm columns, copper concentration was 2 times higher than the control. It can be concluded that at increased soil depths, copper leaching would be minimal and that MGDA applications at the studied rates would not pose a high risk for leaching into groundwater. It can thus be stated that applications of MGDA are an effective and environmentally safe way to improve copper extraction by O. picensis in these soils.

Subsoil heterogeneities controlling porewater contaminant mass and microbial diversity at a site with a complex pollution history

This study seeks to improve our understanding of the conceptual model of pollutant transport and fate in cases of DNAPL contamination at sites with a complex contamination history. The study was carried out in an unconfined aquifer of alluvial fans in the Tarragona Petrochemical Complex (Spain). Two boreholes were drilled and continuous cores were recovered in order to carry out a detailed core description at centimeter scale and a comprehensive sampling of borehole cores. The biogeochemical heterogeneity at these sites is controlled by the conjunction of lithological, hydrochemical and microbiological heterogeneities. Biodegradation processes of contaminant compounds take place not only at the level of the dissolved fraction in the aquifer but also at the level of the fraction retained in the fine, less conductive materials as shown by the biodegradation haloes of parent and metabolite compounds. Sampling the low-conductivity levels also allowed us to identify compounds, e.g. BTEX, that are the remaining traces of the passage of old contaminant plumes whose sources no longer exist. This enabled us to describe past biogeochemical processes and to partially account for the processes occurring today. Transition zones, characterized by numerous textural changes, constitute ecotones whose biostimulation could be effective in promoting the acceleration of the remediation of the multiple pollution at these sites.

Processes controlling the fate of chloroethenes emanating from DNAPL aged sources in river-aquifer contexts.

This work dealt with the physical and biogeochemical processes that favored the natural attenuation of chloroethene plumes of aged sources located close to influent rivers in the presence of co-contaminants, such as nitrate and sulfate. Two working hypotheses were proposed: i) Reductive dechlorination is increased in areas where the river-aquifer relationship results in the groundwater dilution of electron acceptors, the reduction potential of which exceeds that of specific chloroethenes; ii) zones where silts predominate or where textural changes occur are zones in which biodegradation preferentially takes place. A field site on a Quaternary alluvial aquifer at Torelló, Catalonia (Spain) was selected to validate these hypotheses. This aquifer is adjacent to an influent river, and its redox conditions favor reductive dechlorination. The main findings showed that the low concentrations of nitrate and sulfate due to dilution caused by the input of surface water diminish the competition for electrons between microorganisms that reduce co-contaminants and chloroethenes. Under these conditions, the most bioavailable electron acceptors were PCE and metabolites, which meant that their biodegradation was favored. This led to the possibility of devising remediation strategies based on bioenhancing natural attenuation. The artificial recharge with water that is low in nitrates and sulfates may favor dechlorinating microorganisms if the redox conditions in the mixing water are sufficiently maintained as reducing and if there are nutrients, electron donors and carbon sources necessary for these microorganisms.

Temporal hydrochemical and microbial variations in microcosm experiments from sites contaminated with chloromethanes under biostimulation with lactic acid

ABSTRACT The aim of this research was to identify the sequence of degradation processes that leads to the selective enrichment of microorganisms involved in the degradation of carbon tetrachloride and chloroform under conditions of natural attenuation and lactic acid biostimulation. To this end, a comparative study using microcosm experiments was conducted to analyze these two scenarios. The authors used groundwater and sediment collected from a field site located at a petrochemical complex to create the microcosms. Chemical, compound-specific isotope and microbial analyses were performed. A significant finding of this work was the abiotic degradation of carbon tetrachloride. Another result was the identification of biotic reductive dechlorination of chloroform by a bacterium of the Clostridiales order. This study showed that biostimulation with lactic acid produced faster degradation rates of carbon tetrachloride and chloroform. Lactic acid acted as an electron donor and promoted a decrease in the concentration of other electron acceptors such as nitrate and sulfate, which competed with chloromethanes. Thus, biostimulation could be an efficient remediation strategy for sites contaminated with chloromethanes, especially when a sites complex pollution history results in chemical background concentrations that are high in compounds that could potentially reduce natural attenuation.

Reductive dechlorination in recalcitrant sources of chloroethenes in the transition zone between aquifers and aquitards

In the transition zone between aquifers and basal aquitards, the perchloroethene pools at an early time in their evolution are more recalcitrant than those elsewhere in the aquifer. The aim of this study is to demonstrate that the biodegradation of chloroethenes from aged pools (i.e., pools after decades of continuous groundwater flushing and dissolution) of perchloroethene is favored in the transition zone. A field site was selected where an aged pool exists at the bottom of a transition zone. Two boreholes were drilled to obtain sediment and groundwater samples to perform chemical, isotopic, molecular, and clone library analyses and microcosm experiments. The main results were as follows: (i) the transition zone is characterized by a high microbial richness; (ii) reductively dechlorinating microorganisms are present and partial reductive dechlorination coexists with denitrification, Fe and Mn reduction, and sulfate reduction; (iii) reductively dechlorinating microorganisms were also present in the zone of the aged pool; (v) the high concentrations of perchloroethene in this zone resulted in a decrease in microbial richness; (vi) however, the presence of fermenting microorganisms supplying electrons for the reductively dechlorinating microorganisms prevented the reductive dechlorination to be inhibited. These findings suggest that biostimulation and/or bioaugmentation could be applied to promote complete reductive dechlorination and to enhance the dissolution of more nonaqueous phase liquids (DNAPL).