Absorption of toxic chemicals

Inhalation (into the lungs). This is a more common pathway for the absorption of toxic chemicals these may be in the form of gases, vapours, dusts or mists. All toxic powders, volatile liquids and gases should only be handled in efficient fume cupboards. The practice of sniffing the vapours of unknown compounds for identification purposes should be conducted with caution. 

There are many different animal models that have been used to assess the percutaneous absorption of toxic chemicals. There is little question that while in vivo human studies are best for predicting the absorption of percutaneous applied chemical warfare agents, ethics preclude conducting such studies. Rats have been widely used in the study of skin contamination, wounds, and healing and the efficacy of different decontamination modalities (Wester and Maibach, 2000 Shah et al, 1987 Baynes et al., 1997). 

Many organic compounds, such as cyanides, and most aromatic amines, amides, and phenols can produce systemic poisoning by direct contact with the skin. Absorption of toxic chemicals through the skin and eyes is the next most important route of entry after inhalation. 

Do these operations have the potential for skin absorption of toxic chemicals and wastes ... 

Formulation. The formulation of a material may have a significant influence on its potential to cause toxic injury. Eor example, solvents may facihtate or retard the penetration and absorption of a chemical, resulting in enhancement or suppression of a toxic response, respectively. 

Measurement of exposure can be made by determining levels of toxic chemicals in human serum or tissue if the chemicals of concern persist in tissue or if the exposure is recent. For most situations, neither of these conditions is met. As a result, most assessments of exposure depend primarily on chemical measurements in environmental media coupled with semi-quantitative assessments of environmental pathways. However, when measurements in human tissue are possible, valuable exposure information can be obtained, subject to the same limitations cited above for environmental measurement methodology. Interpretation of tissue concentration data is dependent on knowledge of the absorption, excretion, metabolism, and tissue specificity characteristics for the chemical under study. The toxic hazard posed by a particular chemical will depend critically upon the concentration achieved at particular target organ sites. This, in turn, depends upon rates of absorption, transport, and metabolic alteration. Metabolic alterations can involve either partial inactivation of toxic material or conversion to chemicals with increased or differing toxic properties. 

Interactions between chemicals may be of a physico-chemical and/or biological nature. Examples of physico-chemical interactions are the reaction of nitrite with aUcylamines to produce carcinogenic nitrosamines, and the binding of toxic chemicals to active charcoal resulting in a decreased absorption from the gastrointestinal tract. It is held that physico-chemical interactions will normally only occur at high doses and therefore are of lesser importance for low-dose scenarios. Physico-chemical interactions will therefore not be considered in any detail in this book. 

Risk assessment and epidemiology could be successfully combined to analyze environmental health risks. Exposure assessments estimate concentrations of toxic chemicals in the environment that could be transferred to humans by ingestion, inhalation, or dermal absorption. In the future, there will be a greater need for agreement on how best to simultaneously assess societal risks involved with damage to both ecosystems and the human population (Ruttenber, 1993). 

The purpose of the gastrointestinal tract is to digest and absorb food. As a result, it is a major site for absorption of xenobiotic chemical substances. Many environmental toxicants enter the food chain and are absorbed together with food. In occupational settings, airborne toxic substances enter the mouth from breathing and, if not inhaled, can be swallowed and absorbed from the gastrointestinal tract. 

Acute toxicity data also can suggest the extent of absorption through different routes of exposure. If, for example, systemic toxicity or death can occur as a result of significant absorption of the chemical through dermal exposure, it must be assumed that dermal exposure also can cause reproductive or developmental toxicity. 

In the case of the absorption of mixtures, one or more of the chemicals may be metabolized at the uptake point producing multiple species for distribution. Even the absorption of small numbers of toxic chemicals can thereby result in the presence of numerous toxic species being distributed to multiple body sites. 

It is beyond the scope of this book to examine all the sources of toxic chemical contamination of foods consumed by humans. The sections that follow address the absorption of xenobiotic chemicals via plant and animal growth and by the addition of toxic chemicals to food during its preparation and packaging. 

Figure 1. A schematic showing how chemicals may enter, be absorbed into, distributed within, and excreted from the body. Adapted in part from C.D. Klaassen, Distribution, Excretion, and Absorption of Toxicants, Chapter 3 of Casarett and Doull s Toxicology (see Recommended Readings).

Chitin is known to be biodegradable, biocompatible, and nontoxic. It is used in dmg delivery and bio medical applications. It also used in the purification of water especially for the absorption of toxic dyes. Chitin has limited solubility in solvents but chitosan is readily soluble in acidic aqueous solutions and has more tendency to be chemically modified. Chitosan can readily be spun into fibers, cast into films, or precipitated in a variety of micromorphologies from acidic solutions. Min and Kim have reported on the adsorption of acid dyes from wastewater using composites of PAN/chitosan [52]. Shin et al. has reported on copolymers composed of PVA and poly dimethyl siloxanes cross-linked with chitosan to prepare semi IPN hydrogels for application as biomedical materials... 

Absorption of toxic compounds that may alter thdr own absorption secondary to cutaneous toxieity of the penetrant has been studied using the chemical vesicant sulfur mustard (Riviere et al., 1995). In this model, absorption profiles could ordy be preeisely described if the vascular compartment was modulated as a function of sulfur mustard in the skin. This was independently correlated to vascular volume/pCT-meabihty using inuhn infusions to measure vascular space. 

Drug and chemical dermal absorption typically involves experiments conducted using single chemicals, making the mechanisms of absorption of individual chemicals extensively studied (the subject of most chapters in this volume). Similarly, most risk assessment profiles and mathematical models are based on the behavior of single chemicals. A primary route of occupational and environmental exposure to toxic chemicals is through the skin however, such exposures are often to complex chemical mixtures. In fact, the effects of coadministered chemicals on the rate and extent of absorption of a topically applied systemic toxicant may determine whether... 

Because of its availability, excised animal skin has be used extensively to model percntaneons absorption of drugs and other chemicals in hnmans. Percntaneous absorption of toxic componnds can be measured satisfactorily with excised skin in vitro), but adequate supplies of human skin are not always available. When... 

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