Fate of Chemical Health Hazards

In the process of identifying chemical health hazards, tlie near term and long tenn fate of tlie hazard should be incorporated into tlie analysis. Near-term concerns relate primarily to tlie release of the chemical into the enviromnent. This leads to the general subject area of e.xposure assessment, including routes of e.xposure - a topic that is treated in e.xtensive detail in Cliapter 12. However, tlie fate of the chemical (hazard) following tlie point of human entry is another consideration when attempting to identify health hazards. An overview of tliis topic is presented here 

On tlie otlicr hand, tlie liver is not protected, and its total potential absorption of a chemical is much greater. 

posure route partly determines the distribution of the chemical in die body. Like tlie chemical benzene, a single chemical may follow multiple routes of e. posure. The liver, like the skin, acts as a filter. The liver is the primary dcto.xification site. To.xicants that arc absorbed into the lungs, skin, mouth, and esophagus may temporarily bypass the liver however, toxicants absorbed tluougli the stomach and intestines follow the blood s direct path to tlie liver. 

The site of accumulation may define tlie point of toxic action. Inorganic mercury accumulation in the kidneys causes sever functional impairment Kidney damage has been shown to occur when the accumulated total of cadmium in the kidney cortex reaches 100-200 ppm 

These iiicchanisnis can affect the near-term and ultimate fate of a chemical hazard. Recognition of these inechanisms can significantly assist in the identification of a chemical agent as a health hazard. In recent years, the understanding of chemical transport, chemical manipulation in the body, and response by animals luid humans to cheniicals has advtmccd to a point where it is possible to determine whether a chemical is indeed a health hazard. 

Paustcnbadi lias provided mi e.xcellcnt review of the physical and chemical properties of substances mid how tliis information is used to predict tlie 

As one miglit expect. c. posure to a chemical compels a response by the human body. The body responds to a chemical with physiological (metabolic) processes in order to absorb, distribute, store, transform, or eliminate tliat chemical. To become a chemical health hazard, tlie chemical or tlie transformation of that chemical by the body must reach a target organ for a sufficient length of time and at a sufficient concentration to produce toxic effects. A target organ is tlic preferential anatomical site for the expression of toxic effects by a chemical substance in tlie human body. 

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Section 10.7 Fate of Chemical Health Hazards Section 10.8 Carcinogens versus Non-carcinogens... 

The process of identifying chemical healtli liazards should also incorporate the near term (release into tlie environment) and long term fate of the chemical health hazard following entry into the human body. Non-carcinogcnic effects include all toxicological responses except tumors. Not all tumors are cancerous. Malignant tumors are cancerous and spread, or metastasize, to surrounding structures. 

Chemical Manufacturing Process Product Formulation Environmental Fate Summary Human Health Hazards Summary Environmental Hazards Summary Chemistry of Use Process Description Process Safety Assessment Market Information International Information... 

Our lack of knowledge regarding the fate of chemicals in the aquatic environment has resulted often in poorly defined issues and confused public concern regarding the hazards of pesticides to human health and our environment. We already have seen evidence of increasing legislative... 

The EPA s Office of Pollution Prevention and Toxics developed Chemical Fact sheets to summarize information on a particular chemical including exposure, environment and human health hazard, environmental fate, regulatory information, and whom to contact for additional information. 

This book is intended to be a handbook to which the reader will frequently refer for details of estimation methods appropriate for the chemicals of interest. It is intended primarily for anyone involved with estimating chemical properties, but particularly those who need such data for environmental or health assessment of chemical substances. It will also be of interest to engineers, research scientists, and educators who are concerned with the fate and effects of hazardous substances. 

The assessment which is undertaken by NICNAS covers the assessment of the health and aquatic toxicity hazards of the chemical, occupational exposure, public exposure and environmental exposure and fate. A risk assessment is performed and recommendations are made to control and minimise the risks. The results of the assessment are published in a report which is made available to the public via the NICNAS Web site [3]. 

A further OECD Council Decision in 1991 focused on HPV chemicals. These decisions prompted the development of a minimum hazard data set to describe an HPV chemical - the Screening Information Data Set, or SIDS. This includes physicochemical properties (melting point, boiling point, vapor pressure, water solubility, and octanol-water partition coefficient) environmental fate (stability in water, photodegradation, biodegradation, and an estimate of distribution/transport in the environment) environmental effects (acute toxicity to aquatic vertebrates, invertebrates, and plants) and human health effects (acute toxicity, repeated-dose toxicity, toxicity to the gene and the chromosome, and reproductive and developmental toxicity). 

Chemical mass transfer responsible for partitioning of contaminants constitutes a significant part of the processes involved in the transport and fate of contaminants. In the longer term, the redox environment (pE) and subsequent reduction-oxidation reactions will ultimately determine the final fate of the contaminants. The assessment of whether retention or retardation processes are responsible for the observed partitioning and hence the attenuation of contaminants within the soil matrix, is vital and critical in the evaluation of the natural attenuation capability of the soil barrier system. The dilemma facing both regulatory agencies and practitioners is obvious If potential pollution hazards and threats to public health and the environment are to be minimized or avoided, How can one ensure that the processes for contaminant attenuation in the substrate are the result of (irreversible sorption) retention... 

A number of species have been designated hazardous air pollutants (HAPs) or toxic air contaminants (TACs). Most are directly emitted into the air, but some also have significant secondary sources, i.e., are formed by chemical reactions in air. Furthermore, the ultimate health impacts are determined not only by the emissions and formation of such compounds in air but also by their atmospheric fates. In short, some pollutants react in air to form less toxic species, whereas others form more toxic compounds. Thus, scientific risk assessments of these pollutants require an accurate and complete understanding of their atmospheric chemistry. Some specific examples are discussed in this chapter. 

Less than half of the new chemical submissions received by the EPA contain any kind of test data. The EPA can obtain and review whatever toxicity or physical data on the new chemical happen to be available, such as data from literature sources, but usually there are none. For most new chemical submissions, measured values for chemical, toxicological, or environmental fate properties are not available for the E PA to use to make decisions regarding hazards or risks that the chemical may pose to human health or the environment, or its global impact. 

On July 24, 2008, the EPA published a proposed test rule under Section 4 of TSCA for 19 chemical substances.33 The proposed testing for each chemical under the proposed rule is deemed necessary by EPA to inform various data needs that will provide critical information about the environmental fate and potential hazards associated with these chemicals. The data will be used in conjunction with data on exposure and uses to evaluate potential health and environmental risks. 

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