Nitrate controls methyl mercury production in a streambed bioreactor

Organic carbon bioreactors provide low-cost, passive treatment of a variety of environmental contaminants but can have undesirable side effects in some cases. This study examines the production of methyl mercury (MeHg) in a streambed bioreactor consisting of 40 m3 of wood chips and designed to treat nitrate (NO?) in an agricultural drainage ditch in southern Ontario (Avon site). The reactor provides 30 to 100% removal of NO?-N concentrations of 0.6 to 4.4 mg L(-1), but sulfate (SO?(2-)) reducing conditions develop when NO? removal is complete. Sulfate reducing conditions are known to stimulation the production of MeHg in natural wetlands. Over one seasonal cycle, effluent MeHg ranged from 0.01 to 0.76 ng L(-1) and total Hg ranged from 1.3 to 3.4 ng L(-1). During all sampling events when reducing conditions were only sufficient to promote NO?(-) reduction (or denitrification) ( = 5, late fall 2009, winter 2010), MeHg concentrations decreased in the reactor and it was a net sink for MeHg (mean flux of -5.1 μg m(-2) yr(-1)). During all sampling events when SO?(2-) reducing conditions were present ( = 6, early fall 2009, spring 2010), MeHg concentrations increased in the reactor and it was a strong source of MeHg to the stream (mean flux of 15.2 μg m(-2) yr(-1)). Total Hg was consistently removed in the reactor (10 of 11 sampling events) and was correlated to the total suspended sediment load ( r2 = 0.69), which was removed in the reactor by physical filtration. This study shows that organic carbon bioreactors can be a strong source of MeHg production when SO?(2-) reducing conditions develop; however, maintaining NO?-N concentrations > 0.5 mg L suppresses the production of MeHg.     

Field test of a cross-injection scheme for stimulating in situ denitrification near a municipal water supply well

A pilot-scale test of an in situ denitrification scheme was undertaken to assess an adaptation of the nutrient injection wall (NIW) technology for treating a deep (30-40 m) nitrate contamination problem (N-NO(-)(3) ~ 10-12 mg/L). The adaptation is called the Cross-Injection Scheme (CIS). It duplicates the NIW method without a wall; wells are installed and operated directly in the aquifer and high-flux zones of the aquifer are preferentially targeted for treatment. The test was conducted on the site of a municipal water supply well field, with the supply well pumping between 15-80 m(3)/h. Acetate was periodically injected into the aquifer between an injection-extraction well pair positioned across the normal direction of flow. The injected pulses were then permitted to move with the water toward the municipal wells, providing a carbon supply to drive the desired denitrification. The fate of nitrate, nitrite, acetate and sulphate were monitored at multilevel wells located between the injection location and the municipal wells. The acetate pulsing interval was approximately weekly (9 h injections), so that the system was operating passively 95% of the time. Previous work on the site has established that the highest solute fluxes were associated with a 1-3 m thick zone about 35 m below surface. This zone was found to respond to the acetate additions as a function of the municipal pumping rate and the carbon-to-nitrogen ratio (i.e., determined by the injected acetate concentration). Initially, acetate was injected just below the theoretical stoichiometric requirement for complete denitrification and nitrate disappearance was accompanied by nitrite production. Increasing the C:N ratio (doubling the acetate injection concentration) increased the removal of nitrate and diminished the occurrence of nitrite. Slowing the municipal pumping rate, with a C:N ratio of 1.2-1.6, resulted in complete nitrate attenuation with no nitrite production and no sulfate reduction. The experiment demonstrated that the CIS injection scheme is a viable option for the treatment of nitrate contamination in situ near high-capacity wells.     

Trends in the elemental composition of fine particulate matter in Santiago, Chile, from 1998 to 2003

Santiago, Chile, is one of the most polluted cities in South America. As a response, over the past 15 yr, numerous pollution reduction programs have been implemented by the environmental authority, Comisión Nacional del Medio Ambiente. This paper assesses the effectiveness of these interventions by examining the trends of fine particulate matter (PM(2.5)) and its associated elements. Daily fine particle filter samples were collected in Santiago at a downtown location from April 1998 through March 2003. Additionally, meteorological variables were measured continuously. Annual average concentrations of PM(2.5) decreased only marginally, from 41.8 microg/m3 for the 1998-1999 period to 35.4 microg/m3 for the 2002-2003 period. PM(2.5) concentrations exceeded the annual U.S. Environmental Protection Agency standard of 15 microg/m3. Also, approximately 20% of the daily samples exceeded the old standard of 65 microg/m3, whereas approximately half of the samples exceeded the new standard of 35 microg/m3 (effective in 2006). Mean PM(2.5) levels measured during the cold season (April through September) were three times higher than those measured in the warm season (October through March). Particulate mass and elemental concentration trends were investigated using regression models, controlling for year, month, weekday, wind speed, temperature, and relative humidity. The results showed significant decreases for Pb, Br, and S concentrations and minor but still significant decreases for Ni, Al, Si, Ca, and Fe. The larger decreases were associated with specific remediation policies implemented, including the removal of lead from gasoline, the reduction of sulfur levels in diesel fuel, and the introduction of natural gas. These results suggest that the pollution reduction programs, especially the ones related to transport, have been effective in reducing various important components of PM(2.5). However, particle mass and other associated element levels remain high, and it is thus imperative to continue the efforts to improve air quality, particularly focusing on industrial sources.     

Deposition, Verteilung sowie Bedeutung für den Menschen und sein Nahrungsnetz

Since the introduction of automotive exhaust catalysts in 1984, an intensive discussion started about the emission of platinum group metals and their effect on mankind and the environment. Several platinum compounds are known to be potent sensitizers, even at very small doses. In spite of both the scientific and public interest in this important field, the collection and coordination of scientific research and its conclusions continues to be a lacking. The present results from analytical chemistry, ecology, toxicology and occupational medicine are summarized here. This state of the art indicates the great need for further investigations concerning especially the assessment of emission sources and bioavailability studies for platinum as well as palladium and rhodium.     

Thriving at work: A meta‐analysis

Thriving at work refers to a positive psychological state characterized by a joint sense of vitality and learning. On the basis of Spreitzer and colleagues' model, we present a comprehensive meta‐analysis of antecedents and outcomes of thriving at work (K = 73 independent samples, N = 21,739 employees). Results showed that thriving at work is associated with individual characteristics, such as psychological capital (r_c = .47), proactive personality (r_c = .58), positive affect (r_c = .52), and work engagement (r_c = .64). Positive associations were also found between thriving at work and relational characteristics, including supportive coworker behavior (r_c = .42), supportive leadership behavior (r_c = .44), and perceived organizational support (r_c = .63). Moreover, thriving at work is related to important employee outcomes, including health‐related outcomes such as burnout (r_c = ?.53), attitudinal outcomes such as commitment (r_c = .65), and performance‐related outcomes such as task performance (r_c = .35). The results of relative weights analyses suggest that thriving exhibits small, albeit incremental predictive validity above and beyond positive affect and work engagement, for task performance, job satisfaction, subjective health, and burnout. Overall, the findings of this meta‐analysis support Spreitzer and colleagues' model and underscore the importance of thriving in the work context.     

Seeking Indigenous food sovereignty: origins of and responses to the food crisis in northern Manitoba,Canada

A food crisis confronts many Indigenous communities in northwestern Canada, as reflected by wide-scale food insecurity and diet-related disease. South-generated responses to this crisis generally disregard principles of Indigenous food sovereignty and are disengaged from concerns related to environmental and food justice. This study seeks to explore the needs and priorities of a First Nation (Misipawistik Cree Nation) and an associated Métis community (Grand Rapids) regarding existing and potential responses to the food crisis in northern Manitoba. Substantial changes to the traditional food system were initiated during the establishment of the reserve system in the 1800s and now extend to damage associated with hydro development. Responses to these changes were categorised according to themes and include the revival of country food traditions, individual and community gardens, agriculture in the North, and better quality imported foods. Regardless of response, decision-making needs to be community-driven, culturally appropriate, to reflect local priorities in order to effectively address the northern food crisis, and, ultimately, needs to work towards Indigenous food sovereignty to be effective.