GIS-based approach to zoning the risk associated with municipal solid waste management: application to regional scale.

The objective of this paper is to offer an approach to assess the risk associated with Municipal Solid Wastes, in a geospatial context. Initially, a risk index including hazard, vulnerability and other important variables was built. The built model is based on multi-criteria evaluation techniques and geographic information systems. Subsequently, the constructed index was used to model possible damage in various municipalities of the state of Chiapas, Mexico. The results indicate that the highest levels of risk are found in places with unfavorable conditions, such as high rates of waste generation, low waste collection coverage, steep slopes, etc. that cover 6.22% of the study area. The areas with high risk level are mainly found in the southeast of the municipalities of Villa Corzo and Villaflores, and cover 27.06% of the study area. The places of low and very low risk levels are concentrated in the center and northeast of the study area, in the municipalities of Suchiapa, Chiapa de Corzo and Acala, and cover 38.6% of the area. At the municipal level, Berriozábal, Villaflores and Villa Corzo have the highest levels of risk in most of their territory; the high levels of risk presented in Berriozábal are due to the limited territorial area that it occupies in the study area. In Villaflores and Villa Corzo, the high levels of risk are due to the high population dispersion. A large part of Tuxtla Gutiérrez territory presents low and medium risk levels, especially within the population settlement. The peripheral areas show the highest levels of risk, because the waste collection service is not provided very often. Finally, the Cohen's kappa statistic used to validate the precision of the model gave a value of 0.34, which means that the spatial model can be considered acceptable despite its low value. Although this work is only a general approach to spatial risk modeling at a regional scale, it provides interesting information. Moreover, it adds to the few efforts that exist in the literature to model the risk associated with wastes.

Organophosphorus and Organochlorine Pesticides Bioaccumulation by Eichhornia crassipes in Irrigation Canals in an Urban Agricultural System.

A natural wetland in Mexico City Metropolitan Area is one of the main suppliers of crops and flowers, and in consequence its canals hold a high concentration of organochlorine (OC) and organophosphorus (OP) pesticides. There is also an extensive population of water hyacinth (Eichhornia crassipes), which is considered a plague; but literature suggests water hyacinth may be used as a phytoremediator. This study demonstrates bioaccumulation difference for the OC in vivo suggesting their bioaccumulation is ruled by their log K(ow), while all the OP showed bioaccumulation regardless of their log K(ow). The higher bioaccumulation factors (BAF) of the accumulated OC pesticides cannot be explained by their log K(ow), suggesting that the OC pesticides may also be transported passively into the plant. Translocation ratios showed that water hyacinth is an accumulating plant with phytoremediation potential for all organophosphorus pesticides studied and some organochlorine pesticides. An equation for free water surface wetlands with floating macrophytes, commonly used for the construction of water-cleaning wetlands, showed removal of the pesticides by the wetland with room for improvement with appropriate management.

Conostegia xalapensis (Melastomataceae): an aluminum accumulator plant.

In acidic soils, an excess of Al³âº is toxic to most plants. The Melastomataceae family includes Al-accumulator genera that tolerate high Al³âº by accumulating it in their tissues. Conostegia xalapensis is a common shrub in Mexico and Central America colonizing mainly disturbed areas. Here, we determined whether C. xalapensis is an Al accumulator, and whether it has internal tolerance mechanisms to Al. Soil samples collected from two pastures in the state of Veracruz, Mexico, had low pH and high Al³âº concentrations along with low Ca²âº levels. Leaves of C. xalapensis from pastures showed up to 19,000 mg Al kg⁻¹ DW (dry weight). In laboratory experiments, 8-month-old seedlings treated with 0.5 and 1.0 mM AlCl3 for 24 days showed higher number of lateral roots and biomass. Pyrocatechol violet and hematoxylin staining evidenced that Al localized in epidermis and mesophyll cells in leaves and in epidermis and vascular pith in roots. Scanning electron microscope-energy dispersive X-ray microanalysis of Al-treated leaves corroborated that Al is in abaxial and adaxial epidermis and in mesophyll cells (31.2%) in 1.0 mM Al-treatment. Roots of Al-treated plants had glutathione reductase (EC 1.6.4.2) and superoxide dismutase (EC 1.15.1.1) activity higher, and low levels of O2*⁻ and H2O2. C. xalapensis is an Al-accumulator plant that can grow in acidic soils with higher Al³âº concentrations, and can be considered as an indicator species for soils with potential Al toxicity.