PRINCIPLES OF TOXICOLOGY - Biology East Borneo

16.13 TOXIC PROPERTIES OF REPRESENTATIVE HALOGENATED SOLVENTS 397Local application of carbon tetrachloride to human skin produces distinct pain with erythema,hyperemia, and wheal formation followed by vesiculation, which may facilitate secondaryinfection. Studies have indicated that absorption of carbon tetrachloride through the skin maypresent a potential problem based on a limited study on human subjects. In view of the potentialhepatotoxicity of carbon tetrachloride, repetitive contact of the skin with liquid carbon tetrachlorideshould be prevented.Vinyl chloride (see Figure 16.24) is a gas under ambient conditions, and is a potent skin irritant.Contact with the liquid form may cause frostbite. The eyes may be immediately and severely irritated.Vinyl chloride depresses the central nervous system, causing symptoms that resemble mild alcoholintoxication. Lightheadedness, nausea, and dulling of visual and auditory responses may develop inacute exposures. Severe vinyl chloride exposure has been reported to result in death. Workers enteringpolyvinyl chloride reactor vessels for cleaning have exhibited a triad combining arthro-osteolysis,Raynaud’s phenomenon, and scleroderma. Chronic exposure may damage the liver and induce a highlyspecific liver cancer (angiosarcoma), which is an established risk for chronic exposures to vinylchloride at the old TLV ® of several hundred ppm. Increased rates of cancer of the lung, lymphatic, andnervous systems have been reported. Experimental evidence links vinyl chloride to tumor inductionin a variety of organs, including liver, lung, brain, and kidney, and to nonmalignant alterations (fibrosis,connective tissue deterioration).Figure 16.24 Vinyl chloride.The mutagenic, carcinogenic, and reproductive hazard of vinyl chloride is further discussed inChapters 11, 12, and 13, respectively.Trichloroethene (TCE) and perchloroethene (PERC) (see structures in Figure 16.25) are among themost widely used chlorinated solvents, on an historical basis. The toxicological literature is extremelylarge for these substances, and the reader is referred to the ATSDR Toxicological Profiles for a moredetailed treatment of available information. These substances exhibit a generally low degree of acutetoxic potential, and industrial use experience has been relatively good in cases where appropriateexposure controls were in place. Although historically both have been regulated as potentialcarcinogens by some occupational and environmental regulatory agencies, recently the ACGIHreclassified TCE in Group A5 (Not Suspected as a Human Carcinogen, and placed PERC in ClassA3 (Animal Carcinogen). The classification for both of these agents by U.S. EPA is under reviewat this time. It is of interest to note that in some environmental conditions both TCE and PERCmay be degraded by sequential dechlorination to vinyl chloride, which was described previouslyin this section.Figure 16.25 TCE and PERC.