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

The response of different types of soils 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 of between 0 and 5000 mg kg-1of 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 ED50 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 ED50 values, which better reflect the alteration of a soil due to the presence of a xenobiotic substance.Peer reviewe

Carbono orgânico dissolvido e biodisponibilidade de N e P como indicadores de qualidade do solo

Nas últimas décadas, qualidade do solo tem se tornado um tópico importante na ciência do solo. Embora esforços consideráveis tenham sido dedicados com o intuito de definir "qualidade do solo", ainda não há um conceito amplamente aceito pela comunidade cientifica. A seleção de índices qualitativos para definir qualidade do solo é uma tarefa extremamente difícil, e diversas propriedades químicas, físicas e biológicas tem sido sugeridas como potenciais indicadores. A matéria orgânica do solo está associada com processos químicos, físicos e biológicos no solo, e, portanto, é considerada um dos melhores indicadores de qualidade do solo. O manejo do solo pode influenciar significativamente a dinâmica do carbono orgânico e o ciclo de N, P, e S. Entretanto, mudanças na concentração total da matéria organica em resposta ao manejo pode ser dificil de ser detectada devido à variabilidade natural do solo. Quando comparada com a matéria orgânica total do solo, a fração mais prontamente disponível, como o carbono orgânico dissolvido (COD), é mais sensível às mudanças no manejo do solo a curto e médio prazo e, portanto, pode ser utilizada como indicador fundamental de qualidade do solo ou das alterações das condições naturais. Embora a fração dissolvida represente apenas uma pequena porção da matéria orgânica total do solo, o COD é móvel no solo e constitui uma importante fonte de C para os microorganismos, podendo facilmente refletir os efeitos de diferentes sistemas de manejo. Inúmeros métodos são utilizados para caracterizar o COD, mas os processos que influenciam sua mineralização e a disponibilidade dos elementos associado com a matéria orgânica (N, P, e S) ainda não são completamente entendidos. Pesquisas futuras devem buscar entender os processos que governam a dinâmica de nutrientes e do COD e como os mesmos afetam a qualidade do solo.Soil quality has become an important issue in soil science. Considerable attempts have been made to define soil quality, but a general concept has not yet been accepted by the scientific community. The selection of quantitative indices for soil quality is extremely difficult, and a considerable number of chemical, physical, and biochemical properties have been suggested as potential indicators of soil quality. Because soil organic matter (SOM) can be associated with different soil chemical, physical and biological processes, it has been widely considered as one of the best soil quality indicator. Land use can significantly influence dynamics of organic carbon and N, P, and S cycle. However, changes in total soil organic carbon (SOC) contents in response to land use may be difficult to detect because of the natural soil variability. In the short to medium term, biological properties and readily decomposable fractions of SOC, such as dissolved organic carbon (DOC), are much more sensitive to soil management than is SOM as a whole, and can be used as a key indicator of soil natural functions. Despite the fact that labile C accounts for a small portion of the total organic matter in the soils, DOC is the most mobile and important C-source for microorganisms, and can easily reflect the effects of land use on soil quality. Although several methods are used to characterize DOC, the factors influencing mineralization and bioavailability of elements associated with organic matter (N, P, and S) remains unclear. Future research should focus on the processes that govern DOC and nutrient dynamics and how they affect soil quality

Environmental risk assessments for transgenic crops producing output trait enzymes

The environmental risks from cultivating crops producing output trait enzymes can be rigorously assessed by testing conservative risk hypotheses of no harm to endpoints such as the abundance of wildlife, crop yield and the rate of degradation of crop residues in soil. These hypotheses can be tested with data from many sources, including evaluations of the agronomic performance and nutritional quality of the crop made during product development, and information from the scientific literature on the mode-of-action, taxonomic distribution and environmental fate of the enzyme. Few, if any, specific ecotoxicology or environmental fate studies are needed. The effective use of existing data means that regulatory decision-making, to which an environmental risk assessment provides essential information, is not unnecessarily complicated by evaluation of large amounts of new data that provide negligible improvement in the characterization of risk, and that may delay environmental benefits offered by transgenic crops containing output trait enzymes

Hydrolytic enzyme activities in agricultural and forest soils. Some implications for their use as indicators of soil quality

Although a great deal of information exists about the effect of land use on soil enzyme activities, much of this is contradictory and brings into question the suitability of soil enzyme activities as indicators of how land use affects soil quality. The purpose of this study was to investigate the effect of land use on different soil biochemical properties, especially hydrolytic enzyme activities, with the aim of providing knowledge about the problems related to the use of enzymes as indicators of soil quality. The data presented derive from various studies in which a large number of soils under different types of forest or agricultural management were analysed by the same methods. All of the soil samples were characterized in terms of their main physical and chemical properties, the activity of several hydrolases, microbial biomass C and soil basal respiration. The results indicate that soil use causes a large reduction in organic matter content and that the effect on enzyme activity varies depending on the type of land use or management and the type of enzyme. Furthermore, the enzyme activities per carbon unit (specific activities) in soils affected by land use are almost always higher than in maximum quality soils (climax soils under oak vegetation or oak soils), and land use also generates greater increases in the specific activity as the C content decreases. The mechanism responsible for these increases probably involves loss of the most labile organic matter. Enzyme enrichment is not always produced to the same degree, as it varies as a function of the enzyme and the type of land use under consideration. It is concluded that the complexity of the behaviour of the soil enzymes raises doubts about the use of enzyme activities as indicators of soil degradation brought about by land use.This research was financed by the Xunta de Galicia (Project No. XUGA 40003B94) and by the Spanish Ministerio de Ciencia y Tecnología (Project No. BTE 2001-0987).Peer reviewe

Thermodynamic parameters of enzymes in grassland soils from Galicia, NW Spain.

39: 311-319.The thermodynamic parameters of the enzymes catalase, dehydrogenase, casein-protease, a-N-benzoyl-L-argininamide (BAA)- protease, urease, Carboxymethyl (CM)-cellulase, invertase, b-glucosidase and arylsulphatase, were investigated in grassland soils from a European temperate-humid zone (Galicia, NW Spain). The effect of temperature on enzyme activity was determined at 5, 18, 27, 37, 57 and 70 1C. The temperature-dependence of the rate of substrate hydrolysis varied depending on the enzyme and soil. In general, the soil containing the least amount of organic matter (OM) showed the lowest enzyme activity for all temperatures and enzymes, whereas soils with similar OM contents showed similar levels of activity for the entire temperature range. Temperature had a noteworthy effect on the activity of oxidoreductases. Product formation in the reaction catalyzed by dehydrogenase increased with increasing temperature until 70 1C, which was attributed to chemical reduction of iodonitrotetrazolium violet (INT) at high temperatures. Catalase activity was not affected above 37 1C, which may be explained either by non-enzymatic decomposition of hydrogen peroxide or by the fact that catalase has reached kinetic perfection, and is therefore not saturated with substrate. The Arrhenius equation was used to determine the activation energy (Ea) and the temperature coefficient (Q10) for all enzymes. The values of Ea and Q10 for each enzyme differed among soils, although in general the differences were small, especially for those enzymes that act on substrates of low molecular weight. In terms of the values of Ea and Q10 and the differences established among soils, the results obtained for those enzymes that act on substrates of high molecular weight differed most from those corresponding to the other enzymes. Thus the lowest Ea and Q10 values corresponded to BAA-protease, and the highest values to CM-cellulase and casein-protease. Except for catalase in one of the soils, the values of Ea and Q10 for the oxidoreductases were similar to those of most of the hydrolases. In general, the effect of temperature appeared to be more dependent on the type of enzyme than on the characteristics of the soil. r 2006 Elsevier Ltd. All rights reserved.Peer reviewe

Hydrolitic enzyme activities in agricultural and forest soils. Some implications for their use as indicators of soil quality.

40: 2146-2155.Although a great deal of information exists about the effect of land use on soil enzyme activities, much of this is contradictory and brings into question the suitability of soil enzyme activities as indicators of how land use affects soil quality. The purpose of this study was to investigate the effect of land use on different soil biochemical properties, especially hydrolytic enzyme activities, with the aim of providing knowledge about the problems related to the use of enzymes as indicators of soil quality. The data presented derive from various studies in which a large number of soils under different types of forest or agricultural management were analysed by the same methods. All of the soil samples were characterized in terms of their main physical and chemical properties, the activity of several hydrolases, microbial biomass C and soil basal respiration. The results indicate that soil use causes a large reduction in organic matter content and that the effect on enzyme activity varies depending on the type of land use or management and the type of enzyme. Furthermore, the enzyme activities per carbon unit (specific activities) in soils affected by land use are almost always higher than in maximum quality soils (climax soils under oak vegetation or oak soils), and land use also generates greater increases in the specific activity as the C content decreases. The mechanism responsible for these increases probably involves loss of the most labile organic matter. Enzyme enrichment is not always produced to the same degree, as it varies as a function of the enzyme and the type of land use under consideration. It is concluded that the complexity of the behaviour of the soil enzymes raises doubts about the use of enzyme activities as indicators of soil degradation brought about by land use.Peer reviewe

Effect of soil use on the composition of circulating water: the Fonte Espiño river basin (Galicia, NW Spain).

En Difusse Phosphorus Loss (eds. Goswin Heckrath and Gitte H. Rubaek), págs. 397-399.Peer reviewe