Natural Environmental Exposure

Natural environmental exposure, the exposure of materials or products to natural environmental conditions, can be regarded as a form of simulated service testing. Such exposures provide information on the durability of the material without the effects of such factors as fatigue and abrasion. 

Evans,R.D., Harley,J.H., Jacobi,W., McLean,A.S., Mills,W.A. and C.G. Stewart, Estimate of Risk from Environmental Exposure to Radon-222 and its Decay Products, Nature 290 98 (1981). 

Studies with lambda-cyhalothrin and the freshwater crustacean G. pulex have shown that shorter durations of exposure result in substantially less severe effects than maintained, long-term exposures [15], In this case there was a significant reduction in toxicity with decreasing exposure times, with an 18-fold reduction in toxicity with exposure for 1 h compared to that determined after exposure for 96 h. Given this inverse correlation with exposure duration and toxicity, effects under natural environmental conditions where water column concentrations of pyrethroids are expected to decrease relatively rapidly are again likely to be less than would be predicted from estimates of toxicity under standard laboratory conditions with maintained concentrations (see Sect. 5). 

The introduction of estrogens and progestogens into the environment is a function of the way several factors are combined. The manufactured quantity and the dosage applied (amount, frequency, and duration) combined with the excretion efficiency of the compound and its metabolites, the capability of adsorption and desorption on soil, and the metabolic decomposition in sewage treatment are examples of necessary factors to assess environmental exposure. In general the fate and effect of a substance in the environment is dependent on the distribution into the different natural systems, such as air, water, and solids (soil, particles, sediment, and biota). Information on the physical and chemical properties (Ku, Kd, and Kim vapor pressure) of a compound may help determine whether it is likely to concentrate in the aquatic, terrestrial, or atmospheric... 

Strictly, natural exposure can be carried out for any of the environmental agents. For example, if the product is to spend its life in water at 70 °C then exposure to water at 70 °C can be considered natural ageing. Exposure to water at 80 °C could be called natural ageing at worst possible conditions or with a safety factor. Natural exposure defined in this way is carried out by adapting the standard laboratory methods for air ageing and exposure to liquids as there are no specific natural exposure standards. 

Estimates of service life are usually made either by natural or simulated trials or, most commonly, by accelerated tests with extrapolation to predict performance at longer times under less severe conditions. An alternative approach is to subject the product to environmental exposures which equate to the whole design life, and then to assess performance by real or simulated service tests (the end performance assessment). The exposures usually have to involve accelerated procedures and can be composed of several environmental agents applied simultaneously or sequentially. 

As long as chemical regulation is based on this risk-based philosophy, human and environmental exposure to dangerous chemicals - substances of very high concern - will continue. The disperse and dilute model does not work for persistent bioaccumulative chemicals because Nature quite simply collects and concentrates these materials overtime. 

Ruckstuhl, S. (2001) Environmental Exposure Assessment of Sulfonated Naphthalene Formaldehyde Condensates and Sulfonated Naphthalenes Applied as Concrete Superplasticizers, Doctor of Natural Sciences Dissertation to Swiss Federal Institute of Technology, Zurich, Switzerland. 

There is steady growing evidence that environmental exposure to insects at home and in the workplace are the frequent causes of allergic sensitization (Arlian 2002). Subsequently clinical symptoms are mainly of respiratory nature, manifested in allergic rhinitis, asthma, and urticaria (Steen et al. 2004), and in some documented cases also via ingestion, causing systemic anaphylaxis. 

Descriptive and analytic study designs are observational in nature, in that children cannot be randomly assigned to receive the environmental exposure (e.g. chemical). Analytic study designs are... 

Warfarin. Warfarin is a popular rodenticide particularly common in rat poison preparations. Because of its toxic nature, assessment of workplace and environmental exposures is of concern. Warfarin can be quickly and easily determined by reverse phase HPLC. Details of the procedure applied in our laboratory are as follows ... 

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