RESUMO
In this study, two Lactuca sativa crops grown in a net-protected site and an unprotected site were compared. The results showed metals were accumulated by Lactuca sativa. Higher metal accumulation in lettuce grown in the unprotected parcel was established, and the only significant differences in their physicochemical properties were cation exchange capacity and exposure to sunlight. Exposure to the sun may translate into higher soil-plant flux of water and/or higher decomposition rate of organic matter, which may augment the mobilization of metals into the plant, and therefore lead to higher noxious metal accumulation on the crops. Also, EDTA was explored as a possible extractant that could predict the bioavailablity of metals to the lettuce. Our results did not show a good agreement between the metal transferred from soil to leaves and the EDTA extracted metals, although some tendencies were found for the metal transfer from soil to roots. It is predicted that many developing countries will continue and/or increase the use of waste water for the irrigation of crops despite the health risks. Different solutions have been explored to diminish the availability of the metals in the soils. Our study shows that an action as simple as placing a net over the parcel could help diminish the accumulation of metals into the crops of a rapidly expanding peri-urban agricultural system.
Assuntos
Lactuca/metabolismo , Metais/metabolismo , Poluentes Químicos da Água/metabolismo , Agricultura , Disponibilidade Biológica , Cidades , Ácido Edético/química , Monitoramento Ambiental , Substâncias Húmicas , Metais/química , México , Solo/análise , Poluentes Químicos da Água/químicaRESUMO
This study evaluated the spatial and temporal distribution of metals in the coral reef system Cayos Arcas and Triangulos in the Campeche Bank region, off the Yucatan peninsula in Mexico. No information has been generated before for the incorporation of natural and non-natural occurring metals, some of which are possibly endowed by the oil marine station Cayo Arcas. The multivariate exploratory study of the metals on the coral skeletons, showed the formation of two distinct groups. The metals that have the highest influence on the differentiation of the groups are the metals that are natural constituents of the coral skeletons, in particular Sr can explain much of the differences between the groups, and to a much lesser extent are the metals that could be indicators of pollution. This differentiation suggests that, in our case, the environment around the corals has a higher impact than the non-naturally occurring metals (and possible indicators of pollution). The two groups formed corresponded to: the coral cores influenced by open sea variables and the coral cores in the inner part of the keys which is less exposed to open sea variables. A chronological study was made to two samples that had the longest coral section and were situated in two clearly distinctive zones: an exposed surface subjected to high wave forces and another that was less exposed. Ni and Zn show an accumulation trend in both coral samples, while Ba showed an increase in incorporation around 1980 when the Cayo Arcas oil marine station was constructed.
Assuntos
Antozoários/química , Ecossistema , Metais/análise , Água do Mar/química , Poluentes Químicos da Água/análise , Animais , Antozoários/anatomia & histologia , Monitoramento Ambiental/métodos , Humanos , México , Oceanos e MaresRESUMO
Possible contaminants produced by the Petroleos Mexicanos (PEMEX) marine oil complex in the vicinity of the Cayo Arcas (Mexico) coral reef ecosystem were evaluated by analyzing sediments and sea water for hydrocarbons and metal elements. We found that the concentrations of aliphatic hydrocarbons in the sea water were generally low, with the highest values detected near the oil station; the concentration of polycyclic aromatic hydrocarbons (PAHs) was generally below the detection limit. The hydrocarbons found in the sediments seem to have a pyrogenic origin, and were probably produced by marine traffic in the study area. The total PAH concentration did not exceed the NOAA criteria, although levels of some individual PAHs did. The only metal detected in the sea water at high concentrations was nickel. The Ni/V ratio in the sediments indicates the contribution of crude oil to the system. The high content of Ni and Zn was attributed to the ballast waters from the oil tankers that load at the station's monobuoys. The presence of fine sediments that commonly originate from terrestrial ecosystems supported this assumption.
Assuntos
Antozoários/química , Ecossistema , Petróleo , Hidrocarbonetos Policíclicos Aromáticos/análise , Oligoelementos/análise , Poluentes Químicos da Água/análise , Animais , Monitoramento Ambiental , Sedimentos Geológicos/química , México , Níquel/análise , Água do Mar/análise , Zinco/análiseRESUMO
A land suitability study was carried out by applying a multiple-criteria technique to 12 different vegetation types in Mexico's Tamaulipas state to help select potentially suitable sites for hazardous waste treatment plants. Species richness, spatial distribution, and uniqueness were selected as the criteria for estimating a vegetation type's suitability. Using the analytical hierarchy process, we ranked and mapped vegetation types, then compared the results with rankings of the same vegetation types based only on their number of endemic species. The suitabilities of the various vegetation types were ordered in more or less the same way by both methods, except in two cases for which the results were very different. The method proved to be a useful tool despite the availability of only partial (mostly qualitative) information; under such circumstances, expert experience can be incorporated in the evaluation process to a limited degree. The technique described in this paper has a high potential to aid decisions when many opinions and options must be considered simultaneously.
Assuntos
Ecossistema , Monitoramento Ambiental , Resíduos Perigosos/efeitos adversos , Plantas Comestíveis/crescimento & desenvolvimento , Gerenciamento de Resíduos/métodos , Poluição Ambiental , Geografia , México , Plantas Comestíveis/classificação , Dinâmica Populacional , Medição de Risco , Solo/normasRESUMO
Dehydrogenase activity (DHA) in soils contaminated by arsenic-bearing tailings was correlated with total arsenic and total water-soluble arsenic (As(III)+As(V)) to evaluate the impact of tailings dispersion on the oxidative capacity of soil microorganisms. Georeferenced surface soil samples (0-10 cm depth) were collected at different distances from a tailings dam. In the samples farthest from the dam, all water-soluble arsenic (avg. 0.6+/-0.1 mg kg(-1)) was As(V). The highest concentration of water-soluble As(III)+As(V) (>1.9 mg kg(-1)) was found where As(III) was present. DHA averaged 438.9+/-79.3 microg INTF g(-1) h(-1) at the greatest distance from the dam and decreased to 92.3+/-27.1 microg INTF g(-1) h(-1) with decreasing distance from the dam. Pearson correlation coefficient between DHA and samples containing water-soluble As(V) (r=-0.87) was greater than that between DHA and total water-soluble arsenic (r=-0.57). The correlation between DHA and soluble arsenic containing both As(V) and As(III) was not significant (r=0.24). In soils with detectable As(III) concentrations where wet conditions prevail (i.e., reducing conditions), there is an abiotic response in addition to a biotic one. The correlation between DHA and total water-soluble As(III)+ As(V) was higher (r=-0.79) when the abiotic response was excluded. Our study demonstrated the importance of distinguishing between total and available fraction and its species and the need to evaluate biological functions in addition to purely geochemical analyses. DHA bioassay combined with other microbial properties offers a good tool for evaluating soil microbial activity and status and is a suitable indicator of the oxidative capacity of soil microorganisms affected by tailings in an oxidizing environment; however, under reducing conditions, abiotic responses must also be studied.