Sublethal effects

Studies of 30-60 days duration with three comparatively sensitive species of freshwater Ashes demonstrated that concentrations of 1.0 and 3.0 xg Cd/L in water of low alkalinity caused reductions in growth, survival, and fecundity of brook trout (Salvelinusfontinalis), the most sensitive species tested. Under conditions of increasing alkalinity, the maximum allowable cadmium concentration range for brook trout increased to 7.0 and 12.0 p-g/L a similar case was made for the walleye (Stizostedion vitreum vitreum). Among all species of freshwater biota examined, cadmium concentrations of 0.47-5.0 pg/L were associated with decreases in standing crop. 

One of the more sensitive indicators of cadmium exposure is the inhibition of non-thioneine hepatic metal-binding proteins inhibition was observed in juvenile bluegills 

Sublethal effects in birds are similar to those in other species and include growth retardation, anemia, renal effects, and testicular damage. However, harmful damage effects were observed at higher concentrations when compared to aquatic biota. For example, Japanese quail (Coturnix japonica) fed 75.0 mg Cd/kg diet developed bone marrow hypoplasia, anemia, and hypertrophy of both heart ventricles at 6 weeks. In zinc-deficient diets, effects were especially pronounced and included aU of the signs mentioned plus testicular hypoplasia a similar pattern was evident in cadmium-stressed quail on an iron-deficient diet. In aU tests, 1% ascorbic acid in the diet prevented cadmium-induced effects in Japanese quail. In studies with Japanese quail at environmentally relevant concentrations of 10.0 p,g Cd/kg BW daily (for 4 days, administered orally), absorbed cadmium was transported in blood in a form that enhanced deposition in the kidney less than 0.7% of the total administered dose was recovered from liver, kidneys, and duodenuna. 

In wood ducks (Aix sponsa) fed rations containing 10.0 mg Cd/kg, no renal effects were noted although kidneys contained 62.0 mg Cd/kg FW. Renal damage was noted when 

0 mg Cd/kg ration for 12 weeks, blood chemistry was altered, and mild to severe kidney lesions developed. But mallard juveniles were unaffected when given diets containing 

---

Neurotoxic compounds can have behavioral effects in the field (see Chapters 5, 9, and 15), and these may reduce the breeding or feeding snccess of animals and their ability to avoid predation. A number of the examples that follow are of sub-lethal effects of pollutants. The occurrence of sublethal effects in natural populations is intimately connected with the question of persistence. Chemicals with long biological half-lives present a particular risk. The maintenance of substantial levels in individuals, and along food chains, over long periods of time maximizes the risk of sublethal effects. Risks are less with less persistent compounds, which are rapidly... 

From an ecotoxicological point of view, it has often been suspected that sublethal effects, such as those described here, can be more important than lethal ones. Both p,p -DDT and p,p -DDD are persistent neurotoxins, and may very well have caused behavioral effects in the field. This issue was not resolved when DDT was widely used, and remains a matter for speculation. More is known, however, about eggshell thinning caused by p,p -DDE and its effects upon reproduction, which will be discussed in Section 5.2.5.I. 

FIGURE 5.6 Dieldrin intoxication in hnmans and its relationship to blood levels. The hatched area represents the sublethal effects seen at 15-30% of lethal threshold concentration in blood (after Jager 1970). 

Thus, there is not a great deal of difference between the three classes in acute toxicity all are highly toxic. However, methyl mercury is more persistent than the other two types, and so has the greater potential to cause chronic toxicity. The latter point is important when considering the possibility of sublethal effects. 

The following brief account identifies only major groups of herbicides not mentioned elsewhere in the text, and is far from comprehensive. Their mode of action is only dealt with in a superficial way. From an ecotoxicological point of view, there has not been as much concern about their sublethal effects upon plants as there has been in the case of mammals, and there has not been a strong interest in the development of biomarker assays to establish their effects. The major concern has been whether weeds, or nontarget plants, have been removed following herbicide application—a rather easy matter to establish as plants are fairly sedentary. For a more detailed account of herbicide chemistry and biochemistry, see Hassall (1990). 

Jefferies. D.J. (1975). The role of the thyroid in the production of sublethal effects by organochlorine insecticides and PCBs In Moriarty (Ed.). Organochlorine Insecticides Persistent Organic Pollutants 132-230, London Academic Press. 

Moriarty, F.M. (1968). The toxicity and sublethal effects of p-p -DDT and dieldrin to Aglais urticae and Chorthippus brunneus. Annals of Applied Biology 62, 371-393. 

Thompson, H.M. and Mans, C. (2007). The relevance of sublethal effects in honey bee testing for pesticide risk assessment. Pest Management Science 63, 1058-1061. 

Weisbart, M. and Eeiner, D. (1974). Sublethal effect of DDT on osmotic and ionic regnlation by goldfish Carassius auratus. Canadian Journal of Zoology—Revue Canadienne De Zoologie 52, 739-744. 

Calabrese A, Thurberg FP, Dawson MA, WenzlofF DR. 1975. Sublethal physiological stress induced by cadmium and mercury in the winter flounder (Pseudoplumnectes amer-icanus). In Koeman JH, Strik JJ, editors, Sublethal effects of toxic chemicals on aquatic animals. Amsterdam Elsevier. 

Aniline may be absorbed following inhalation, ingestion, and dermal exposures. The inhalation toxicity of aniline was studied in several animal species, but only one study that utilized multiple exposure concentrations for sublethal effects was located. Data from human studies lack specific details or exposures... 

---