Statistical investigation of polychlorinated dibenzo-p-dioxins and dibenzofurans in the ambient air of Houston, Texas

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (dioxins and furans) are persistent, bioaccumulative and highly toxic chemical constituents that appear in the environment at very low and difficult to measure levels. Although dioxins and furans are widely recognized as toxic contaminants needing regulation, their temporal and spatial concentration profiles and the factors impacting their partitioning and congener distribution are only moderately understood. This paper presents the results from one of the most extensive ambient air dioxin and furan sampling efforts conducted in a geographic area to date. The data consist of monthly ambient concentrations of 17 of the most toxic congeners of dioxins and furans collected at five locations in Houston, Texas over a calendar year. The results showed a total annual mean dioxin and furan congener concentration of 1047 fg/m3 and an annual mean summation operatorI-TEQ concentration of 15 fg I-TEQ/m3 (16 fg WHO-TEQ/m3). These results, when compared with proximate data from the USEPA National Dioxin Ambient Monitoring Network (NDAMN), revealed significant (at the P0.05 level) differences between Houston and the NDAMN sites, suggesting the existence of local dioxin sources. A temporal analysis of the data showed that the congener concentration distribution varies over time, depending on the level of chlorination, type of congener, and temperature. The results also suggested that the fluctuations of congener concentrations and I-TEQ concentrations are closely correlated with minimum relative humidity, mean temperature, and mean NOx concentration.     

Negative interactions between two SW Atlantic intertidal crabs in soft-bottom habitats

The intertidal crabs Chasmagnathus granulatus and Cyrtograpsus angulatus coexist across the SW Atlantic intertidal. Previous studies in this region suggest that C. granulatus displace C. angulatus in soft sediment, where C. granulatus build burrows (“burrowing beds”). We examined variation in abundance, size-frequency distribution, sex ratio, incidence of autotomies, and diet of both species in C. granulatus crab beds and adjacent areas without burrows. We also experimentally tested the hypothesis that in the absence of C. granulatus, C. angulatus will build burrows. Only large sized individuals of C. angulatus venture into C. granulatus crab beds. The sex ratio of C. angulatus was always biased towards females, with higher bias outside crab beds (1:8 outside, 1:2 inside). Although the items consumed in the crab beds did not differ from those consumed outside, the males of C. angulatus had a higher frequency of empty stomachs in crab beds. The incidence of limb autotomies of C. angulatus was higher outside C. granulatus crab bed areas. After a long rainy period in which C. granulatus was absent from these areas, the pattern of habitat use of C. angulatus changed. During this period C. angulatus showed higher abundance in the areas, where C. granulatus previously constructed burrows, and there were no differences between areas in any of the measured parameters. In the absence of C. granulatus, C. angulatus built their own burrows and never used C. granulatus burrows. The interaction between C. granulatus and C. angulatus may be a good example of competitive exclusion, when the shared resource is the access to surface soft-sediment.     

Carbon Monitoring Costs and their Effect on Incentives to Sequester Carbon through Forestry

Technically, forestry projects have thepotential to contribute significantly tothe mitigation of global warming, but manysuch projects may not be economicallyattractive at current estimates of carbon(C) prices. Forest C is, in a sense, a newcommodity that must be measured toacceptable standards for the commodity toexist. This will require that credible Cmeasuring and monitoring procedures be inplace. The amount of sequestered C that canbe claimed by a project is normallyestimated based on sampling a number ofsmall plots, and the precision of thisestimate depends on the number of plotssampled and on the spatial variability ofthe site. Measuring C can be expensive andhence it is important to select anefficient C-monitoring strategy to makeprojects competitive in the C market. Thispaper presents a method to determinewhether a forestry project will benefitfrom C trading, and to find the optimalmanagement strategy in terms of forestcycle length and C-monitoring strategyA model of an Acacia mangiumplantation in southern Sumatra, Indonesiais used to show that forestry projects canbe economically attractive under a range ofconditions, provided that the project islarge enough to absorb fixed costs.Modeling results indicate that between 15and 38 Mg of Certified Emission Reductions(CERs) per hectare can be captured by thesimulated plantation under optimalmanagement, with optimality defined asmaximizing the present value of profitsobtained from timber and C. The optimalcycle length ranged from 12 to 16 years andthe optimal number of sample plots rangedfrom 0 to 30. Costs of C monitoring (inpresent-value terms) were estimated to bebetween 0.45 (Mg C)^-1 to 2.11 (MgC)^-1 depending on the spatialvariability of biomass, the variable costsof C monitoring and the discount rate.     

Ritter’s dry-bed dam-break flows: positive and negative wave dynamics

Dam-break flood waves are associated with major environmental disasters provoked by the sudden release of water stored in reservoirs. Ritter found in 1892 an analytical solution to the wave structure of an ideal fluid released during an instantaneous dam failure, propagating over initially dry horizontal terrain. This solution, though ideal, hence frictionless, is widely used to test numerical solutions of the Shallow Water Equations (SWE), and as educational tool in courses of fluid mechanics, given that it is a peculiar case of the Riemann problem. However, the real wave structure observed experimentally differs in a major portion of the wave profile, including the positive and negative fronts. Given the importance of an accurate prediction of the dam break wave, the positive and negative wave portions originating from the breaking of a dam with initially dry land on the tailwater reach are revisited in this work. First, the propagation features of the dry-front are investigated using an analytical boundary-layer type model (Whitham/Dressler/Chanson model) constructed matching an (outer) inviscid dynamic wave to an (inner) viscous diffusive wave. The analytical solution is evaluated using an accurate numerical solution of the SWE produced using the MUSCL-Hancock finite-volume method, which is tested independently obtaining the solution based on the discontinuous Galerkin finite-element method. The propagation features of the negative wave are poorly reproduced by the SWE during the initial stages of dam break flows, and, thus, are then investigated using the Serre–Green–Naghdi equations for weakly-dispersive fully non-linear water waves, which are solved using a finite volume-finite difference scheme.     

Heavy metal content in rubbish bags used for separate collection of biowaste

The heavy metal content of several rubbish bags used to collect the organic fraction of municipal solid waste (OFMSW) is shown in this paper. Nowadays, several public awareness campaigns carried out by municipalities have promoted rubbish bags based mainly on their appearance, without concern for their heavy metal content. A high amount of heavy metals was detected in some polyethylene bags promoted in different campaigns for OFMSW source-sorted collection, while compostable bags presented low quantities of heavy metals. Some other rubbish bags, as well as commercial bags, were also analysed for comparison. These results should be taken into account before promoting the use of one or other type of bag. Moreover, the rubbish bag manufacturers should reduce the heavy metal content in order to avoid heavy metal scattering in the environment, and also to reduce the consumption of raw materials.     

Junk mail in residential homes in the United States: Insights from a sub-urban home in California

Although systematic studies tracking junk mail sent to residential homes are lacking, available reports indicate it is a growing problem in many urban centers worldwide. Junk mail increases the number of trees harvested each year, consumes a substantial amount of energy, causes pollution to air, water and soil and wastes a substantial amount of time sorting, mailing and recycling. Junk mail collected at one residence in the United States for a period of one full year is analyzed to find out the main contributors to this urban problem, what residents should do to reduce or eliminate it. Results indicate that three major businesses are responsible for over 70% of total junk mail sent (n = 1255) including credit card, mortgage and insurance corporations. To encourage environmental sustainability, several strategies that can help businesses reduce junk mail are suggested including new advertising techniques, use of other outlets like billboards, outreach events in social functions and adopting eco-friendly techniques in any junk mail production. Considering the revenue and jobs created from junk mail business, and the absence of government regulation and lack of consensus amongst individuals, environmental groups and businesses on what needs to be done; individuals are urged to explore ways to mitigate the problem and a number of recommendations are given.     

Geochemistry of leachates from the El Fraile sulfide tailings piles in Taxco, Guerrero, southern Mexico

Leachates from the El Fraile tailings impoundment (Taxco, Mexico) were monitored every 2 months from October 2001 to August 2002 to assess the geochemical characteristics. These leachates are of interest because they are sometimes used as alternative sources of domestic water. Alternatively, they drain into the Cacalotenango creek and may represent a major source of metal contamination of surface water and sediments. Most El Fraile leachates show characteristics of Ca–SO₄, (Ca+Mg)–SO₄, Mg–SO₄ and Ca–(SO₄+HCO₃) water types and are near-neutral (pH=6.3–7.7). Some acid leachates are generated by the interaction of meteoric water with tailings during rainfall events (pH=2.4–2.5). These contain variable levels of SO₄ ²⁻ (280–29,500 mg l⁻¹) and As (<0.01–12.0 mg l⁻¹) as well as Fe (0.025–2352 mg l⁻¹), Mn (0.1–732 mg l⁻¹), Zn (<0.025–1465 mg l⁻¹) and Pb (<0.01–0.351 mg l⁻¹). Most samples show the highest metal enrichment during the dry seasons. Leachates used as domestic water typically exceed the Mexican Drinking Water Guidelines for sulfate, hardness, Fe, Mn, Pb and As, while acidic leachates exceed the Mexican Guidelines for Industrial Discharge Waters for pH, Cu, Cd and As. Speciation shows that in near-neutral solutions, metals exist mainly as free ions, sulfates and bicarbonates, while in acidic leachates they are present as sulfates and free ions. Arsenic appears as As^(V) in all samples. Thermodynamic and mineralogical evidence indicates that precipitation of Fe oxides and oxyhydroxides, clay minerals and jarosite as well as sorption by these minerals are the main processes controlling leachate chemistry. These processes occur mainly after neutralization by interaction with bedrock and equilibration with atmospheric oxygen.