Environment decline

The production and use of PFOS has been greatly curtailed since 2000. Thus, if concentrations of PFOS in the environment decline, the hazard posed to Great Lakes biota should also decrease and not reach critical concentrations. However, there are some uncertainties in this simple hazard assess-... 

Despite the benefits of lead and lead ahoys, the use of these materials is declining rapidly, owing primarily to environmental health and safety factors. Eor many years, lead ahoys were the materials of choice for many corrosive environments, but are now being replaced by stainless steel, plastics, and exotic metals. The toxic nature of lead requires special precautions and handling not necessary with other materials. These requirements have reduced the usage of lead ahoys. 

The popularity of aerosols has been declining. A widely used group of propellants, the fluorinated hydrocarbons, have been restricted in use since it was found that they can harm the environment by reducing the o2one layer of the upper atmosphere (see AiRPOLLUTlON ATMOSPHERIC MODELING Ozone). 

Air pollution control legislation is aimed at protecting human health and the overall environment. It also provides a means of reducing economic losses and a decline in environmental amenity as a consequence of air pollution. ... 

This function expresses a volume production during flame passage which starts slowly, speeds up, and gradually declines again. The flow field generated at time t upon ignition somewhere in the environment can be computed by superposition... 

Here n is an operator of molecular axis orientation. In the classical description, it is just a unitary vector, directed along the rotator axis. Angle a sets the declination of the rotator from the liquid cage axis. Now a random variable, which is conserved for the fixed form of the cell and varies with its hopping transformation, is a joint set of vectors e, V, where V = VU...VL,.... Since the former is determined by a break of the symmetry and the latter by the distance between the molecule and its environment, they are assumed to vary independently. This means that in addition to (7.17), we have... 

Plants may be affected by indirect modifications of the environment. Soil acidification, for example, can cause the leaching of nutrients, and the release of toxic aluminum. These effects may operate together to produce nutrient deficiencies or imbalances to plants. High soil concentrations of aluminum may prevent uptake and utilization of nutrients by plants.Increased availability of aluminum in soils has been implicated as a cause of forest declines in both Europe and the United States, possibly through the toxic effects on small feeder roots 14),... 

Effect of UV on Productivity of the Southern Ocean. Has ozone depletion over Antarctica affected the productivity of the Southern Ocean There is no easy answer. First, one has to take into account the fact that the drastic decrease of ozone over Antarctica has been reported as recently as 1976, a relatively short time in the evolution of the organisms to develop mechanisms to cope with elevated UV. One of the most vexing problems in studying the effects of UV radiation on productivity, is a dearth of historical data on the level of UV. Without these baselines, normal fluctuations could easily be interpreted as decline in productivity. Second, there is a host of biotic and abiotic factors that play significant roles in governing the productivity of the Southern Ocean (40). Ultraviolet radiation is but one more complicating factor to be considered in an already stressful environment. 

The Decline in Mercury Conceruration in Fish from Lake St. Clair, 1970-1976, Report No. AQS77-3, Ontario Ministry of the Environment, Toronto, Ontario, 1977, 85p. 

Obviously, one looks for causes. That declines in one or another species have natural factor etiologies is unequivocal. The demise of American elms and of the chestnut were due to natural factors. Insect infestations, bacterial and fungal diseases, hurricanes, floods, freezes, droughts and many other stresses can cause extensive tree death (5). But in such declines typically only a single species is affected or climatic events caused decline in a delimited area. In almost all declines caused by natural events, the causal factors can be identified we know their precise etiologies. Natural events are always part of the natural environment and must be factored in when evaluating forest declines (Table I). 

So far as the discipline of ecotoxicology goes, there have been a number of cases where organic pollutants were shown to be the principal or sole cause of population declines in the natural environment, and these are described in the chapters that... 

PCBs have been implicated in the decline of certain populations of fish-eating birds, for example, in the Great Lakes of North America. Although their use is now banned in most countries and very little is released into the environment as a consequence of human activity, considerable quantities remain in sinks (e.g., contaminated sediments and landfill sites), from which they are slowly redistributed to other compartments of the environment. There continues to be evidence that PCB residues are still having environmental effects, for example, on birds and fish. 

Engstrom DR, Swain EB. 1997. Recent declines in atmospheric mercury deposition in the upper Midwest. Environ Sci Technol 31(4) 960-967. 

---