Dose levels sublethal

In a study of calves dosed with diisopropyl methylphosphonate at 62.5, 125, 250, 500, or 1,000 mg/kg via gelatin capsules placed with a balling gun, calves at the highest dose level displayed pulmonary emphysema upon autopsy (Palmer et al. 1979). No respiratory effects were observed at sublethal dose levels. 

One negative effect of pesticide use is how they stimulate suppressed species. For example, DDT and several other pesticides may accelerate the development of suppressed species (just as they did with the spider mites) and increase the frequency with which new generations are born. Sublethal doses of dieldrin and parathion do not decrease the Colorado beetle s egg production - they increase it by 33-65% in a way we do not yet understand [3]. Data from 1976 showed that using carbofurans increased the Colorado beetle population in several U.S. states [20]. Trichlorfon also stimulates the Colorado beetle s development at specific dose levels. 

In another study of acute-duration, HDI, undiluted or as a solution with peanut oil, was administered via gavage to male albino ChR-CD rats, in single doses from 12 to 3,400 mg/kg, one rat per dose level. Rats receiving high sublethal doses of 1,000 and 670, as well as those receiving 450 and 300 mg/kg, were observed to have slowed respiration after dosing (Haskell Laboratory 1961). 

With respect to toxicity, in most cases, tolerance levels do not seem to be based on risk evaluation. To make such risk evaluations possible, more data on occurrence and toxicity of phycotoxins is needed to evaluate the real risk for consumers in order to set suitable tolerance limits. Moreover, until now only data on the acute oral toxicity both in experimental animals and in humans are available for the majority of the toxins. However, studies on repeated exposure to lower sublethal dose levels are desirable. 

In rhesus monkeys (Macaca mulatta), Pb(C2H5)4 has a greater toxic potential than Pb(CH3)4 [70, 76]. Intravenous Pb(CH3)4 doses of 6 mg kg d caused disturbances of patellar reflexes, peripheral nerve damage, and degeneration of skeletal muscle. Transient clinical abnormalities In peripheral nerve reflexes were detected when 1.2 to 2.4 mg kg d were given. All reflexes were normal after a recovery period [70]. Six months at a dose level equivalent to 6 pg kg d of Pb did not induce clinical manifestations of toxicity [76]. No evidence was found that sublethal exposure to Pb(CH3)4 causes permanent damage to any tissue [70, 76]. The rate of clearance of tissue lead is slower for Pb(CH3)4 than for Pb(C2H5)4 [70]. For lead levels in tissue, blood, urine, and feces, see [70, 76]. 

Experimental animals exposed to sublethal doses of cyclodienes show a similar picture, with changes in EEG patterns, disorientation, loss of muscular coordination and vomiting, as well as convulsions, the latter becoming more severe with increasing doses (Hayes and Laws 1991). It is clear from these wide-ranging studies that a number of neurotoxic effects can be caused by cyclodienes at levels well below those that are lethal. In the human studies described here, subclinical symptoms were frequently reported when dieldrin blood levels were in the range 50-100 pg/L, an order of magnitude below those associated with lethal intoxication. 

Reduction in cholinesterase activity levels of various tissues (blood, brain) is one of the earliest signs of chlorpyrifos intoxication. Cholinesterase reductions have been demonstrated in turkeys fed diets containing 50 mg chlorpyrifos/kg (estimated daily dose of 0.7 mg/kg BW) for 20 days (Schlinke et al. 1969) in chickens fed diets of 25 mg/kg (estimated daily dose of 0.94 mg/kg BW) for 20 days (Schlinke 1970) in quail (Coturnix coturnix) given a single (sublethal) esophageal... 

Sublethal. Thiocyanate excretion increased 10X after 10 min and returned to normal levels after 3.5 h the total thiocyanate collected was equivalent to 85% of the administered dose... 

Pentachlorophenol was most toxic and most rapidly metabolized in aquatic environments at elevated temperatures and reduced pH. Adverse effects on growth, survival, and reproduction of representative sensitive species of aquatic organisms occurred at PCP concentrations of about 8 to 80 pg/L for algae and macrophytes, about 3 to 100 pg/L for invertebrates (especially molluscs), and <1 to 68 pg/L for fishes, especially salmonids. Fatal PCP doses for birds were 380 to 504 mg/kg BW (acute oral), >3850 mg/kg in diets, and >285 mg/kg in nesting materials. Adverse sublethal effects were noted at dietary levels as low as 1.0 mg/kg ration. Residues (mg/kg fresh weight) in birds found dead from PCP poisoning were >11 in brain, >20 in kidney, >46 in liver, and 50 to 100 in egg. 

Irradiated small mammals released into the environment had a lower survival rate than laboratory populations, suggesting that the extrapolation from laboratory results may overestimate the radioresistance of free-ranging voles and other small animals because of the general level of stress in the population (Iverson and Turner 1976). The opposite was observed in eastern chipmunks given high sublethal doses of X-rays. Chipmunks had an overall reduction in mobility when they were released... 

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