FIA-coupled spectrophotometric method for determination of Cr (VI) traces in natural waters: application of in-line dissolution of 1,5-diphenylcarbazide after heat treatment and activated alumina as adsorbent for preconcentration

This work proposes the quantification of Cr (VI) ions in natural waters in trace level, using activated alumina (Al₂O₃) as preconcentration support, controlled in-line dissolution of the solidified chromophore diphenylcarbazide after heat treatment and spectrophotometric detection. The manifold ensures high sensitivity of analytical response, good repeatability, and stability. In this work, optimization of experimental conditions of a flow injection system was chosen as the parameters for greater sensitivity and better selectivity. The selected optimized conditions were 0.30 mol L^?1 for H₂SO₄ concentration, system flow rate as 0.40 mL min^?1, sample injection volume of 192.50 μL, 2 min for preconcentration time, and 0.10 mol L^?1 for eluent concentration. The analytical curves obtained for real sample analysis show linear range from 0.192 to 0.961 μM, linear correlation coefficient R?=?0.9997 and LOD?=?0.024 μM. The preconcentration factor of about four times was obtained through the passage of 800 μL of a standard solution containing 0.961 μM of Cr (VI) through mini-column of preconcentration followed by elution at 192.5 μL of NH₄OH 0.1 mol L^?1 solution. The solid chromogenic reagent presented high durability (weeks in daily use with mass of 0.0993 g) and good reproducibility in analytical signal. The reactivation of the mini-column of alumina should be executed after ten injections of eluent, using 800 μL of HCl 0.02 mol L^?1 solution in flow through the same. Each cycle of injection and elution of the sample takes about 5 min on the proposed terms. Despite the length of each cycle still be high, low concentrations can be detected using a technique of relatively low cost. This is due in part, the association dissolution of the chromogenic reagent directly in the line and the preconcentration step. Another important factor is the economy of reagent chromogenic, low generation of reject contributing to better quality of the environment, and the high potential for applications to work in field.     

The use of Monte-Carlo simulation techniques for risk assessment: study of a municipal waste incinerator

The incremental lifetime risks due to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) for the residents living in the surroundings of a municipal solid waste incinerator (MSWI) have been assessed. Two different pathways of exposure to PCDD/Fs, ingestion through the diet and exposure from MSWI emissions, were compared. Monte-Carlo simulations were carried out to obtain variability and uncertainty propagation The joint analysis of uncertainty and variability included a sensitivity analysis that identified the contribution to variance by different inputs. In general terms, PCDD/F ingestion through the diet contributed with more than 99% of the total risk, whereas direct exposition to PCDD/F emissions from the MSWI was less than 1% The results show that the median (50% percentile) of non-carcinogenic risk due to PCDD/Fs in the population living in the surroundings of the MSWI was 0.72 and the ratio of the 95th percentile and fifth percentile was about 2. With respect to the total carcinogenic risk, the median increment in individual lifetime was 7.90 x 10(-5) while the ratio between the 95th percentile and the fifth percentile was about 1.5. In this analysis, a sequential structural decomposition of the relationships between the input variables has been used to partition the variance in the output (risk) in order to identify the most influential contributors to overall variance among them.     

Health risk assessment of emissions of dioxins and furans from a municipal waste incinerator: comparison with other emission sources

The aim of this study was to calculate the incremental lifetime-risk to dioxins and furans (PCDD/Fs) for the population living in the surroundings of a municipal solid waste incinerator (MSWI), as well as to establish the potential reduction on human health risks as a consequence of the adaptation to the EU legislation on pollutant emissions from the MSWI stack. Analytical and modelled results were obtained. PCDD/F concentrations in environmental media were determined by means of a simple-compartment-multimedia model (air-soil-vegetation model). Predicted and measured PCDD/F concentrations in soils and vegetation were compared, and the effects of MSWI emissions in the environmental media were determined. Human health risks due to PCDD/F emissions from the MSWI were also estimated based on I-TEQ measured and modelled in various environmental media. Cancer risks due to PCDD/F emissions of the plant were 1.07E-07 and 3.08E-09, before and after installation of the clean air system, respectively. On the other hand, cancer risks due to other PCDD/F emission sources in the area were 5.54E-06 and 1.86E-06. Total PCDD/F cancer risks (including those from diet) for the population living in the vicinity of the MSWI were 1.3E-04 and 4.25E-05, respectively (67.6% of reduction). Hazard ratio for total PCDD/F exposure (including diet) decreased during the last 5 years from 1.16 to 0.38. The above data show that other emission sources of PCDD/Fs also have a notable environmental impact on the area under direct influence of the MSWI.     

Polybrominated diphenyl ethers detected in human adipose tissue from Spain

Polybrominated diphenyl ethers (PBDEs) were detected in 13 human adipose tissue samples from Spain, 3 women and 10 men. Tetra-, penta- and hexabrominated diphenyl ethers were determined at ng/g lipid (ppb) level in all the samples. The average TeBDE level was 1.36 ng/g, the average PeBDE was 0.93 ng/g and the HxBDE 1.83 ng/g. Human adipose tissue levels of PBDE obtained in the current samples from Spain are comparable with the tissue levels reported in recent Swedish investigations.     

A novel methodology for determining low-cost fine particulate matter street sweeping routes

This paper addresses the problem of low-cost PM10 (particulate matter with aerodynamic diameter < 10 microm) street sweeping route. In order to do so, only a subset of the streets of the urban area to be swept is selected for sweeping, based on their PM10 emission factor values. Subsequently, a low-cost route that visits each street in the set is computed. Unlike related problems of waste collection where streets must be visited once (Chinese or Rural Postman Problem, respectively), in this case, the sweeping vehicle route must visit each selected street exactly as many times as its number of street sides, since the vehicle can sweep only one street side at a time. Additionally, the route must comply with traffic flow and turn constraints. A novel transformation of the original arc routing problem into a node routing problem is proposed in this paper. This is accomplished by building a graph that represents the area to sweep in such a way that the problem can be solved by applying any known solution to the Traveling Salesman Problem (TSP). As a way of illustration, the proposed method was applied to the northeast area of the Municipality of Santiago (Chile). Results show that the proposed methodology achieved up to 37% savings in kilometers traveled by the sweeping vehicle when compared to the solution obtained by solving the TSP problem with Geographic Information Systems (GIS)--aware tools.     

Seasonal characterization of municipal solid waste (MSW) in the city of Chihuahua,Mexico

Management of municipal solid waste (MSW) has become a significant environmental problem, especially in fast-growing cities. The amount of waste generated increases each year and this makes it difficult to create solutions which due to the increase in waste generation year after year and having to identify a solution that will have minimum impact on the environment. To determine the most sustainable waste management strategy for Chihuahua, it is first necessary to identify the nature and composition of the city’s urban waste. The MSW composition varied considerably depending on many factors, the time of year is one of them. Therefore, as part of our attempt to implement an integral waste management system in the city of Chihuahua, we conducted a study of the characteristics of MSW composition for the different seasons. This paper analyzes and compares the findings of the study of the characterization and the generation of solid waste from households at three different socio-economic levels in the city over three periods (April and August, 2006 and January, 2007).The average weight of waste generated in Chihuahua, taking into account all three seasons, was 0.592 kg capita^?1 day^?1. Our results show that the lowest income groups generated the least amount of waste. We also found that less waste was generated during the winter season. The breakdown for the composition of the waste shows that organic waste accounts for the largest proportion (45%), followed by paper (17%) and others (16%).     

Analysis of Appropriate Timescales for Water Diversion Permits in Brazil

Agreement on the criteria for granting the right to use water resources between governing bodies represents a significant advance in the process of sharing water use. To aid water resource management agencies in optimizing water use, the impact of using different criteria for permitting water use in the Paracatu river basin, Brazil, was evaluated in this study. The streamflow criteria corresponding to 30 % of the annual Q_7,10 (used by the governing body of Minas Gerais), 70 % of the annual Q₉₅ (used by the governing body of the union), 30 % of the monthly Q_7,10, and 70 % of the monthly Q₉₅ were evaluated. The use of criteria based on the monthly streamflow allows for better management of water use because it allows for greater utilization of this resource in times when there is high water availability and imposes a more realistic restriction during critical periods. Substitution of the annual Q_7,10 for the monthly Q_7,10 significantly increases the streamflow permitted in some months, for example, from December to May. Use of the criterion of 70 % of the annual Q₉₅ involves a high risk of drought in critical months, while the criterion of 70 % of the monthly Q₉₅ minimizes this risk.     

A design of two simple models to predict PCDD/F concentrations in vegetation and soils

The vegetation and soil levels of the 17 polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F) toxic congeners were calculated by means of a vegetation and a soil model, respectively. Both models predicted the levels of the 17 PCDD/F congeners in quite good agreement with the observed results although the soil model was more accurate than the vegetation model. Four different pathways of contribution to the vegetation concentrations were taken into account: vapour-phase absorption, dry particle deposition, wet particle deposition and uptake by root. The most important pathway was the vapour-phase absorption and the less was the uptake by root. In the soils model four pathways were considered: background soil concentration, dry particle deposition, wet particle deposition and uptake by root. After the background concentration, the most important pathway was the wet deposition.     

Growth-related intraclonal genetic changes in Gracilaria chilensis (Gracilariales: Rhodophyta)

Gracilaria chilensis exhibits noticeable intraclonal variation, some of which is presumed to result from mitotic recombinations or other types of DNA turnover associated with replication activities during cellular division. To test this, genetic variability (determined by multilocus fingerprinting markers using the randomly amplified polymorphic DNA technique, RAPD) and total growth were simultaneously measured over time in clonal replicates of G. chilensis incubated under controlled laboratory conditions. The results suggest that genetic variability increases as growth occurs and biomass accumulates, supporting the hypothesis of growth-related increases in genetic heterogeneity. For species massively propagated by thallus fragmentation in either naturally or farmed populations, growth-dependent genetic changes may constitute a powerful means of generating intra-population variation without thalli becoming reproductively mature, and, as a consequence, bypassing meiosis and/or sexual recombination. Received: 6 May 1998 / Accepted: 30 July 1999     

Characterization of urban solid waste in Chihuahua, Mexico

The characterization of urban solid waste generation is fundamental for adequate decision making in the management strategy of urban solid waste in a city. The objective of this study is to characterize the waste generated in the households of Chihuahua city, and to compare the results obtained in areas of the city with three different socioeconomic levels. In order to identify the different socioeconomic trends in waste generation and characterization, 560 samples of solid waste were collected during 1 week from 80 households in Chihuahua and were hand sorted and classified into 15 weighted fractions. The average waste generation in Chihuahua calculated in this study was 0.676 kg per capita per day in April 2006. The main fractions were: organic (48%), paper (16%) and plastic (12%). Results show an increased waste generation associated with the socioeconomic level. The characterization in amount and composition of urban waste is the first step needed for the successful implementation of an integral waste management system.