摘要:

During the past decades, the investigation of various elements, species, and isotopes in the frozen atmospheric archives stored in the Greenland and Antarctic ice caps for several hundred thousand years has provided a wealth of fascinating information on past and recent changes in the atmospheric environment of our planet. After a brief description of the Antarctic and Greenland ice caps, we give an overview of the procedures that are used in the field for collecting snow and ice from the surface down to great depths. We discuss the techniques used to date and analyse the samples. The main results obtained to date are then presented, with special emphasis on the very recent. The analysis of the snow and ice layers deposited during the past few centuries, especially since the Industrial Revolution, has allowed us to assess clearly the impact human activity has had on the atmosphere, for important constituents such as heavy metals, sulfur and nitrogen compounds, greenhouse gases, carbon and organic compounds, and artificial radionuclides. The analysis of ancient ice up to several hundred thousand years old has provided unique insight on the past natural changes that affected our atmosphere during glacial–interglacial transitions, especially the temperature, greenhouse gases, soil- and sea-derived aerosols, and heavy metals.Key words: Greenland, Antarctica, ice, global pollution, climate change, heavy metals.

ISSN:1208-6053    

DOI:10.1139/a95-001

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

A critical assessment of the epidemiologic evidence indicates that a real association between aluminum in drinking water and dementia (including Alzheimer's disease, AD) cannot be dismissed. However, all of the study designs had inherent weaknesses and the results could easily be produced by confounding factors. AD appears to be a multifactorial disease in which multiple genes interact with multiple exogenous factors. Genetic loci for AD have been assigned to chromosomes 14, 19, and 21. Head trauma is a recognized environmental risk factor and aluminum in drinking water possibly is another. Aluminum might accelerate the processes involved in AD pathology. Alternatively, it may act as a neurotoxic agent that has independent dementing effects. The positive findings in the drinking water studies would, therefore, constitute an additive phenomenon. Evidence that aluminum is neurotoxic comes from the exposure during dialysis of patients with chronic renal failure and from the mild neuropsychological deficits reported for aluminum workers. Aluminum bioavailability and mass balance considerations indicate that the contribution from drinking water to the daily gastrointestinal uptake of aluminum may not be insignificant. Since renal disease and perhaps age and AD, as well as natural chelating agents, appear to enhance gastrointestinal aluminum absorption, aluminum in drinking water is considered a public health issue. Even though aluminum is unlikely to be responsible for a major burden of illness from dementia, the level of concern warrants stricter enforcement of the 100 μg/L drinking water guideline used in many jurisdictions. Prudent avoidance by the elderly is recommended of products containing potentially bioavailable quantities of aluminum.Key words: aluminum, Alzheimer's Disease, drinking water, human toxicology, epidemiology, absorption, bioavailability.

ISSN:1208-6053    

DOI:10.1139/a95-002

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Restoration of over-fertilized, algae-laden lakes and reservoirs has generally been based on removal or reduction of phosphorus inputs and concentrations. However, this approach frequently is not feasible. An alternative is biomanipulation, in which the biota of the water body, particularly the fish population, is manipulated so as to reduce predation on small herbivorous zooplankters. This results in increases in body size of the zooplankters with consequent great increases in grazing rates on the algae. The process, though controversial, has worked in many lakes and offers promise to many more.Key words: biomanipulation, trophic cascade, lake restoration.

ISSN:1208-6053    

DOI:10.1139/a95-003

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Nickel is present in Canadian freshwater and terrestrial environments because of human activities including mining, smelting, refining, alloy processing, scrap metal reprocessing, other metal operations, fuel combustion, and waste incineration. Nickel can also enter the environment as a result of the natural weathering and leaching of rocks. Entry to the Canadian environment from anthropogenic activities results in measurable concentrations of nickel in various media to which organisms may be exposed. Although current anthropogenic rates of emission per tonne of nickel produced are less than 20 years ago, large quantities are still being emitted to the Canadian environment. Nickel is persistent in terrestrial and aquatic environments. While a large data base is available on concentrations of nickel in freshwater, sediment, soil, and terrestrial plants in Canada, relatively few data on concentrations in aquatic and terrestrial organisms are available. From data collected from 1981 to 1992, most unpolluted rivers and lakes in Canada contained between 0.1 and 10 μg nickel/L with the exception of the naturally elevated site of Smoking Hills, N.W.T. (which is at least three orders of magnitude greater), while industrial sites generally contained between 50 and 2000 μg nickel/L. Nickel levels in sediment collected from 1983 to 1992 from polluted sites such as the Welland River, some Sudbury lakes, and Hamilton and Toronto Harbours ranged between 20 and 5000 μg/g dry weight, while natural or background levels in the Niagara River, Lake Erie, Lake Superior, and Lake Huron were a full two orders of magnitude lower. With respect to drinking water sampled from 1984 to 1991, the trend has been a slight decrease in nickel levels with time but with a greater range emerging, which could be due to more sensitive detection equipment installed in 1986 (minima dropped from 1.0 μg/L to an order of magnitude lower). From data collected from 1984 to 1991, the more urbanization and industrialization associated with the city, the higher the means and medians of nickel levels in air. For example, Halifax, Montréal, Quebec, Windsor, Hamilton, and Toronto had greater air nickel levels than Ottawa, Winnipeg, and Edmonton. This trend was also confirmed with the subgroup of data collected from 1987 to 1990. Sudbury was by far the site with the greatest nickel concentrations (average 124 ng/m3). Furthermore, nickel accumulation in wildlife varied with species. For example, mice seemed to accumulate more nickel in their organs than did rats and other larger rodents, while beavers and minks, on average, accumulated more nickel in their livers than did birds in similar sites near Sudbury. Similar trends have been found in Canadian soil pore water, flora, and soil.Key words: nickel compounds, occurrence, Canadian environment.

ISSN:1208-6053    

DOI:10.1139/a95-004

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The widening use of chromium and its compounds by local industries has led to a growing concern about the effects of chromium contamination on the Canadian environment. This report summarizes the data on Canadian sources and the concentrations of chromium in air, water, sediments, soil, terrestrial wildlife and aquatic biota. It reviews what little is currently known about the cycling of chromium in Canadian ecoystems, and the need for measuring Cr(III) and Cr(VI) rather than total Cr in the environmental media is emphasized. The potential effects of elevated levels of chromium on plants, soil microorganisms, wildlife, and aquatic biota are discussed. The human health effects are not covered. The conclusion is reached that chromium pollution has become a threat to Canadian ecosystems, especially at the local scale where the ambient chromium concentrations in some surface waters, sediments, and soils are now close to or above the toxicity threshold for a number of the more sensistive organisms.Key words: chromium pollution, chromium toxicity, chromium chemistry, chromium emission, bioaccumulation of chromium.

ISSN:1208-6053    

DOI:10.1139/a95-005

出版商:NRC Research Press    

年代:1995

数据来源: NRC