Exposure routes, heavy metals

Recycling of printer circuit boards is deemed as the most important source of heavy metals to the ambient environment. These heavy metals may be entering into human body from various exposure routes such as ingestion, inhalation, and dermal absorption. Exposure to high levels of heavy metals can lead to acute and chronic toxicity, such as damage to central and peripheral nervous systems, blood composition, lungs, kidneys, liver, and even death [14],... 

Metal concentrations and metal activities in the pore water are dependent upon both the metal concentration in the solid phase and the composition of both the solid and the liquid phase. In matrix extrapolation, and with emphasis on the pore water exposure route, it is therefore of great practical importance to have a quantitative understanding of the distribution of heavy metals over the solid phase and the pore water. A relatively simple approach for calculating the distribution of heavy metals in soils is the equilibrium-partitioning (EP) concept (Shea 1988 van der Kooij et al. 1991). The EP concept assumes that chemical concentrations among environmental compartments are at equilibrium and that the partitioning of metals among environmental compartments can be predicted based on partition coefficients. The partition coefficient, Kp, used to calculate the distribution of heavy metals over solid phase and pore water is defined as... 

Perhaps the most difficult aspect of organism behavior to include in media extrapolation procedures is that relating to avoidance. Different species exhibit a diverse array of avoidance behaviors, which they may display in response to natural biotic or abiotic factors in their environment and in response to chemical exposure. Some of the most common include avoidance responses of fish to heavy metals and other contaminants (Sandheinrich 2003), aversion of contaminant-treated diets by birds (Hooper 2003), and drift in stream invertebrates (Sibley et al. 1991 Davies and Cook 1993). Such avoidance behaviors would act to reduce exposure, but are generally ignored in extrapolation approaches. Changes in behavior could potentially have importance in media extrapolation in that they could alter the relative importance of different uptake routes. For example, if a contaminant is partitioned between diet and water, and an exposed species is able to detect and avoid the contaminated food, the relative importance of water as an exposure route could be increased even though total exposure may decrease. 

No toxicity information is available relating to normal routes of occupational exposure. Limits for heavy metals in magnesium stearate have been evaluated in terms of magnesium stearate worst-case daily intake and heavy metal composition. ... 

Although the acute and chronic effects of heavy metals on humans may be well known, knowledge on the sanitary risks connected to their dispersion by aerial routes is still fragmentary. In the vicinity of some industrial emissions of heavy metals in the air (Pb, Hg and Cd) several studies have made evident a risk for the population in the close vicinity of these sources (Donisa et al, 2000). This risk is generally calculated on the basis of the available exposure data by modelling, considering the inhalation and the contamination of soils and water, which is transferred to humans through the food chain. 

A variety of immune alterations have been reported in humans and laboratory animals exposed to other heavy metals, depending on the dose, duration, and route of exposure and genetic susceptibility (Koller, 1980 Ohsawa, 1993 IPCS, 1996). In many studies of subchronic or chronic exposure, non-essential heavy metals such as cadmium, lead, and mercury were immunosuppressive in animals and consequently decreased host resistance to infectious agents and tumours. Immunostimulation has also been shown to occur at levels... 

All carbonyls are highly toxic by all routes of exposure the volatile liquid compounds present additional inhalation risk. Toxicity may be attributed to their decomposition products, the metals and carbon monoxide, essentially the toxic metabolites of all metal carbonyls. Therefore, the unstable carbonyls, especially the mononuclear complexes, which are readily susceptible to breakdown, should be treated as dangerous poisons. The polynuclear carbonyls of heavy metals may bioactivate and exhibit severe delayed effects. Oral intake of such substances can be fatal. The health hazards associated with individual compounds are discussed in the following sections. Toxicity data for most compounds of this class are not available. 

Lead and other heavy metals such as silver, copper, cadmium, lead and bismuth have been known to have toxic effects on humans and our environment since ancient time [3]. These metals have become mainstays in the electronic world in which we live. As a result, human and environmental exposure to these metals has increased significantly over the past several decades, leading to significant health concern and environmental degradation. Lead and other metals enter the environment and the human body through several routes, which environmental and health regulations seek to reduce or eliminate. 

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