Diana Bello

Evaluation of various tests for the diagnosis of soil contamination by 2,4,5-trichlorophenol (2,4,5-TCP)

Soil response to contamination with 2,4,5-triclorophenol was studied to test the validity of the concept of Generic Reference Levels (GRL), the main criterion used to define soil contamination. Soil samples were artificially contaminated with doses between 0 and 5000 mg kg(-1) of 2,4,5-triclorophenol, and analysed by various tests. Where possible, the response of soils to the contaminant was modelled by a sigmoidal dose-response curve in order to estimate the ED(50) values. The tests provided different responses, but only microbial biomass-C and dehydrogenase and urease activities demonstrated soil deterioration in response to contamination. The results suggest that the diagnosis of soil contamination has been greatly simplified in the legislation by the provision of a single figure for each compound, and that the GRL concept could perhaps be substituted by measurement of ED(50) values, which better reflect the alteration of a soil due to the presence of a xenobiotic substance.

Relationships among bulk soil physicochemical, biochemical, and microbiological parameters in an organic alfalfa-rice rotation system

The microbial communities of bulk soil of rice paddy fields under an ancient organic agriculture regimen, consisting on an alfalfa-rice rotation system, were characterized. The drained soil of two adjacent paddies at different stages of the rotation was compared before rice seeding and after harvesting. The relationships among the soil microbial, physicochemical, and biochemical parameters were investigated using multivariate analyses. In the first year of rice cropping, aerobic cultivable heterotrophic populations correlated with lineages of presumably aerobic bacteria (e.g., Sphingobacteriales, Sphingomonadales). In the second year of rice cropping, the total C content correlated with presumable anaerobic bacteria (e.g., Anaerolineae). Independently of the year of rice cropping, before rice seeding, proteolytic activity correlated positively with the cultivable aerobic heterotrophic and ammonifier populations, the soil catabolic profile and with presumable aerobes (e.g., Sphingobacteriales, Rhizobiales) and anaerobes (e.g., Bacteroidales, Anaerolineae). After harvesting, strongest correlations were observed between cultivable diazotrophic populations and bacterial groups described as comprising N2 fixing members (e.g., Chloroflexi-Ellin6529, Betaproteobacteria, Alphaproteobacteria). It was demonstrated that chemical parameters and microbial functions were correlated with variations on the total bacterial community composition and structure occurring during rice cropping. A better understanding of these correlations and of their implications on soil productivity may be valid contributors for sustainable agriculture practices, based on ancient processes.

Laboratory Contamination with 2,4,5-Trichlorophenol: Effects on Some Enzymatic Activities in Two Forest and Two Agricultural Soils of Contrasting pH

Previous studies have shown that different soils deteriorate to different degrees in response to the same amount of 2,4,5-trichlorophenol (2,4,5-TCP) and that enzymatic activities respond in different ways to contamination by this substance. Moreover, the results of these studies suggest that the different behaviour depends on the organic matter content and/or the pH of the soil. The present study was therefore carried out in order to provide further information about the response of soils of contrasting pH to contamination with 2,4,5-trichlorophenol. Two soils developed on limestone with a pH close to the pK of 2,4,5-TCP and two soils developed on acid materials were selected for the study. Soil samples were artificially contaminated with doses of 100 and 500 mg kg−1 of 2,4,5 trichlorophenol and after 72 h were analysed for some oxidoreductase and hydrolase enzyme activities. In general, the enzyme activities appeared to respond in different ways to contamination by trichlorophenol, being the hydrolytic enzymes, mainly invertase, those least affected by the presence of this contaminant. The effect of 2,4,5-TCP was higher in the soils developed on limestone than in the acid soils, thus supporting the idea that pH is one of the key factors that determine the effect of this contaminant on soils.

Extraction and quantification of chlorophenolate molecules in soils spiked with 2,4-dichlorophenol and 2,4,5-trichlorophenol

The compounds 2,4-dichlorophenol (2,4-DCP) and 2,4,5-trichlorophenol (2,4,5-TCP) are classified as priority pollutants, with potentially hazardous impacts on the environment. In soil, dissociation of the phenol group occurs, resulting in the simultaneous presence of neutral phenol and anionic phenolate. Although the toxicity of 2,4-DCP and 2,4,5-TCP to soil microbiota has been suggested to be mainly due to the phenolate anion, this hypothesis cannot be tested due to the lack of appropriate methods of extracting and quantifying the anionic form of these compounds (unlike the neutral form, which can be easily quantified). In this study, we developed a method that enables extraction and quantification of phenolate ions. The method could therefore be used to elucidate the processes that regulate the behaviour of chlorophenolic molecules in soil and to clarify the distribution and toxicity of these compounds in the edaphic environment. The proposed method uses saline solutions (CaCl2, KCl and K2SO4) of low ionic strength to extract the chlorophenolate anion from soil, followed by sequential transformation of the anion from the aqueous solution to an organic solvent that enables subsequent identification and quantification of the molecule by gas chromatography. Two soils of contrasting pH were used to test whether the proposed method was practicable. The method enabled analysis of the distribution of the neutral and anionic forms of the chlorophenols in both types of soil considered and revealed the influence of soil pH in this distribution.

A pH-adjusted method to measure urease activity in soils spiked with tetrafluoroborate 1-butyl-3-methylimidazolium [BMIM][BF 4 ]

ILs commercialization has exponentially increased in recent years because of their very different industrial utilities. Tetrafluoroborate 1-butyl-3-methylimidazolium [BMIM][BF4] is a widely used ionic liquid in different applications. However, the number of studies about the toxic effects of [BMIM][BF4] on the environment is very limited, especially for soils. This is striking since terrestrial ecosystems would be the first to be reached by this compound as a result of any possible accidental spill. Soil biochemical properties, and particularly the enzymatic activities, are very sensitive parameters to detect any perturbation in soil functioning. Among all the enzymes, the urease is one of the most widely used because it is highly sensitive to the presence of different exogenous agents. In this study, we carried out laboratory experiments with two soils of contrasting pH to adjust the parameters and experimental conditions of the method to determine urease activity in soils spiked with [BMIM][BF4].

Effect of sawdust amendment on mineralization of organic nitrogen in a 2,4,5-trichlorophenol contaminated soil

Previous studies have demonstrated that the toxic effects of 2,4,5- trichlorophenol (2,4,5-TCP) are greater in agricultural soils than in forest soils; therefore these effects appear to be influenced by the total C content and soil pH. Agricultural soils (usually low in organic C) contaminated with 2,4,5-TCP may be able to be remediated by the addition of organic waste products. To test this hypothesis, an agricultural soil was artificially contaminated with 5000 mg kg-1, 500 times the Generic Reference Level (GRL) of 2,4,5-TCP, then pine sawdust was added to the contaminated soil at doses equivalent to 5% and 10% of the soil weight. The effect of the sawdust on the toxicity of the contaminant was studied by measuring the degree of mineralization of the organic nitrogen in the soil. The addition of 2,4,5-TCP produced a large increase in the amount of inorganic N present (basically ammoniacal forms), which suggests that the 2,4,5-trichlorophenol caused the death of a large part of the edaphic microbiota. The addition of sawdust buffered this effect, particularly at the highest dose (10%) as the degree of mineralization was similar to that observed in the control sample treated with the same amount of sawdust, this indicating that 10% dose of sawdust is capable of mitigating the toxic effects of 2,4,5-TCP.

Temporal Changes in Some Enzymatic Activities in a Forest and an Agricultural Soils Artificially Contaminated with 2,4,5-Trichlorophenol

The aim of the present study was to investigate the responses of two soils each contaminated with two different doses of 2,4,5-trichlorophenol (2,4,5-TCP), during a period of contact of 24 days, by determining any temporal changes in various enzyme activities. Two soils located close to each other but under different types of management (forest and agricultural) were selected for the study. Several subsamples of each of the soils were contaminated with doses of 2,4,5-TCP of 100 (D100) or 500 (D500) mg kg−1. At 3, 10, 17 and 24 days (3, 10, 17 and 24 d) after addition of the contaminant, analyses were carried out to determine the activities of two hydrolytic (urease and invertase) and two oxidoreductase (catalase and dehydrogenase) enzymes in the contaminated and control soils. The results showed that although the response of the enzymes to the presence of 2,4,5-TCP was very variable, and in some cases almost negligible, the time of contact appeared to heighten the effect, particularly in the agricultural soil.