Latent effect

Latent effects occur either only after there has been a significant period free of toxic signs following exposure, or after resolution of acutely toxic effects which appeared immediately following exposure. They are also referred to as delayed-onset effects. 

If HL (C03-A010) is involved, then exposure of the skin will produce an immediate burning sensation, which may be quickly followed by reddening of the skin (erythema). In addition to other latent effects, casualties exposed to HL may also develop signs of systemic arsenic toxicity including diarrhea, damage to the liver, kidneys, nervous system, and the brain. 

Significant adverse effects of zinc on growth, survival, and reproduction occur in representative sensitive species of aquatic plants, protozoans, sponges, molluscs, crustaceans, echinoderms, fishes, and amphibians at nominal water concentrations between 10 and 25 pg Zn/L (Table 9.6). Latent effects of zinc intoxication after brief exposures are poorly documented. One study showed that sensitive species of freshwater crustaceans exposed to zinc concentrations as low as 150 pg/L for as little as 30 minutes had delayed effects that included increasing immobility for up to 172 hours after exposure (Brent and Herricks 1998). 

Famphur is administered to livestock by intramuscular or subcutaneous injection, through the diet, as a dermal pour-on, or as an oral bolus. In mammals, famphur induced mortality at concentrations as low as 11.6 mg/kg BW in intraperitoneal injection (mouse), 27 mg/kg BW in a single oral exposure (mouse), >33.3 mg/kg BW in an intramuscular injection (Brahman cattle, Bos indicus), and 400 mg/kg BW in a dermal application (rat, Rattus sp.). Latent effects of famphur exposure were reported in reindeer (Rangifer tarandus) hinds 1 year posttreatment (altered blood chemistry). Famphur is rapidly metabolized by mammals. The half-time persistence of famphur and famoxon in subcutaneous fat of cattle after a single pour-on application is 0.9 days and is independent of dose between 25 and 150 mg/kg BW or initial tissue residues between 1.8 and 2.3 mg/kg BW. 

Current recommendations include the discontinuance of topical applications of famphur to cattle because of its association with primary and secondary poisoning of birds — especially magpies, hawks, and eagles — and more research on famphur in the three areas of latent effects on treated livestock, fate and effects in aquatic ecosystems, and carcinogenicity evaluation. 

Eisler, R. 1969. Acute toxicities of insecticides to marine decapod crustaceans. Crustaceana 16 302-310. Eisler, R. 1970a. Latent effects of insecticide intoxication to marine molluscs. Hydrobiologia 36 345-352. Eisler, R. 1970b. Factors Affecting Pesticide-Induced Toxicity in an Estuarine Fish. U.S. Bur. Sport Fish. Wildl., Tech. Paper 45. 20 pp. 

Radiation is carcinogenic. The frequency of death from cancer of the thyroid, breast, lung, esophagus, stomach, and bladder was higher in Japanese survivors of the atomic bomb than in nonexposed individuals, and carcinogenesis seems to be the primary latent effect of ionizing radiation. The minimal latent period of most cancers was <15 years and depended on an individual s age at exposure and site of cancer. The relation of radiation-induced cancers to low doses and the shape of the dose-response curve (linear or nonlinear), the existence of a threshold, and the influence of dose rate and exposure period have to be determined (Hobbs and McClellan 1986). 

Although a number of epidemiological studies have reported an increased risk of lung cancer among occupationally exposed beryllium workers, deficiencies in the studies limit any unequivocal conclusion. Specific criticisms concern the lack of consideration of latent effects, of smoking history, and of exposure to other potential carcinogens and the underestimation of expected lung cancer deaths in comparison populations. "... 

It is important to assess multiple outcomes, since a variety of effects may be correlated if a toxicant has multiple targets or if it has a latent effect. For example, intrauterine growth retardation is a well established correlate for many male reproductive problems, such as testicular cancer (Moller Skakkebaek, 1997), cryptorchidism and hypospadias ( et al., 1999b). The correlation of outcomes is a reflection of the intricate biological interactions of the human organism. 

Spyker JM (1975) Assessing the impact of low level chemicals on development Behavioral and latent effects. Fed Proc, 34 1835-1844. 

The risk assessor should be sensitive to certain dose-response patterns that are often encountered in studies on developmental toxicity. For example, the lowest effective doses in adults and young are often similar or may be the same, but the type of effects may be very different as well, the effects on the developing child may be permanent (or lead to latent effects), whereas the effects on the adult may be transient. Also, the end-points used in evaluating alterations in children s health may vary considerably. The difference between the maternal toxic dose and the developmental toxic dose may at times be related to the relative thoroughness with which end-points are evaluated. Also, the variability and level of severity within a particular end-point need to be defined, since end-point variability and level of severity can have a significant effect on the power of the study and the ability to establish an effect level. Approaches to carrying out dose-response assessments are described below. 

The formation of oxygen anion radicals and molecules of ozone also should be counted with at the ionization initiation of oxidation [26]. Initiation reaction caused by oxygen anion radicals may play an important role within the polymer bulk while the effect of ozone forming in the surrounding air atmosphere will include only the formation of radicals on the polymer surface. The latent effect of ionization initiation on polymer oxidation which is very distinct may be documented on a relatively fast increase of concentration of carbonyl groups, observed over 1 year after irradiation crosslinking of polyethylene [27]. 

Grant-Webster K, BurbacherT, MottetNK. 1992. Puberal growth retardation in primates A latent effect of in utero exposure to methylmercury. Toxicol 12 310. 

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