Sub-lethal effects

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... 

Much of this research could, in concept, be extended to sub-lethal effects. There is already some indication of a relationship between the smoke concentrations that cause death and those that result in physical collapse of the test animals (16). However, more subtle effects, such as decrease in human mental acuity, are expected to be very difficult to assess using rodent data. 

To provide a better understanding of toxic impacts on aquatic ecosystems, cause-effect relationships between changes in biodiversity and the impact of environmental pollution as causative factor as well as the underlying processes. This included the assessment of sub-lethal effects in vitro and in vivo as early warning strategies and of their strength to predict potential hazards to the ecosystem. 

O Halloran, J., A.A. Myers, and P.F. Duggan. 1989. Some sub-lethal effects of lead on mute swan Cygnus olor. Jour. Zool. (London) 218 627-632. 

During exposure to contaminated sediments, test organisms can concentrate chemicals in their tissue and exhibit measurable (sub)lethal effects linked to accumulated substances. In the field of sediment toxicity assessment, it is noteworthy to mention that some studies have been conducted to characterize both exposure and biological effects in parallel. Exposure to contaminants can be gauged by measuring their concentrations in water/sediment and tissue, and effects can be estimated with endpoints such as survival and growth. These studies are important, for example, to detect threshold concentrations at which chemicals begin to exert adverse effects. As such, they can be useful to recommend effective chemical quality standards that will be protective of aquatic life. 

Sprague, J.B. (1971) Measurement of pollutant toxicity to fish III Sub-lethal effects and safe concentrations. Water Research, 5, 245-266. 

The influence of the reference soil on the test result depends on the type of effects measured. Generalisation may be difficult but usually severe effects (lethality) are less influenced by the soil matrix than sub-lethal effects (e.g. mortality of earthworm compared to growth of plants). 

Sub-lethal effects ofTCDD include teratogenicity, carcinogenicity, reproductive complications, suppression of the immune systems, skin lesions and porphyria. Most of these effects have been studied in laboratory animals. 

A number of studies have summarized potential impacts to different types of organisms, including adult fish, developmental fish, zooplankton, and benthic fauna. While earlier studies focused mainly on lethal impacts to coastal fauna exposed to strong acids, recent data have focused on deep-water organisms exposed to CO2, and have included sub-lethal effects. Impacts include respiratory stress (reduced pH limits oxygen binding and transport of respiratory proteins), acidosis (reduced pH disrupts an organism s acid/basis balance), and metabolic depression (elevated CO2 causes some animals to reach a state of torpor). 

These different considerations have led us to assume that this method would be useful to investigate the behavioral effects of toxicants in preference to more natural approaches such as studies in field or semi-field conditions because it allows better control of treatment and conditioning parameters. Indeed, precise quantification of behavior is essential for determining whether a specific non-environmental variable affects the normal behavior. The sublethal effects of chemical pesticides have already been studied using restrained workers in the CPE assay [32-35]. It remains to establish whether the use of the CPE response as a measure of the sub-lethal effects of chemicals on honey bees can be a reliable indicator of the hazards associated with the exposure to sublethal doses of toxic compounds, and consequently can be included in standard screening proce-... 

Measurements of behavioral endpoints in honey bees should provide an effective assessment of hazards caused by crop protection chemicals especially when applied to melliferous plants. Under laboratory conditions, the conditioned proboscis extension (CPE) assay provides detectable sub-lethal effects due to pesticides, and also to gene products potentially used in plant genetic engineering (see other chapters of this book). Impairment in olfactory learning abilities have been shown for chemical concentrations at which no additional mortality occurred. Thus, the use of the CPE assay as a method to evaluate the potential effect on the honey bees foraging behavior can help to assess the toxicity of chemicals in a more comprehensive way than by considering the mortality endpoint alone. The CPE procedure can be used to compare responses to different chemicals (Table... 

Low doses of several compounds, deltamethrin, trichlorfon, and imida-cloprid, tested on M. rotundata and B. terrestris, resulted in various sub-lethal effects repeUency, knock-down, reduced fecundity, longevity or food consumption, and prolonged larval development. 

Tasei, J.N., Lerin, J. and Ripault, G. (2000). Sub-lethal effects of imidacloprid on bumblebees, Bombus terrestris (Hymenoptera Apidae), during a laboratory feeding test. Pest. Manag. Sci. 56, 784-788. 

Lead adversely affected the survival of sensitive mammals tested at different concentrations 5.0-108.0 mg Pb/kg BW in rats (acute oral), 0.32 mg Pb/kg BW daily in dogs (chronic oral), and 1.7 mg Pb/kg diet in horses (chronic dietary). Adverse sub-lethal effects were noted in monkeys given 0.1 mg Pb/kg BW daily (impaired learning 2 years post-administration) or fed diets containing 0.5 mg Pb/kg (abnormal social behavior) in rabbits given 0.005 mg Pb/kg BW (reduced blood ALAD activity) or 0.03 mg Pb/kg BW (elevated blood lead levels) in mice at 0.05 mg Pb/kg BW (reduced ALAD activity) or in sheep at 0.05 mg Pb/kg BW (tissue accumulations). 

Gulec and Holdway studied the toxicity of oil and the dispersant Corexit 9527 to the amphipod, Allorchestes compressa (73). They found that the mean m = 4) acute 96-hour LC50 for A. compressa exposed to Corexit 9527 was 3 mg/L, to dispersed crude oil was 16.2 mg/L, and for the water-accommodated fraction of Bass Strait crude oil was 311,000 mg/L. Sub-lethal effects were also measured for a 30-minute exposure. The EC50 (threshold for sub-lethal effects) was found to be 50.2 mg/L for Corexit 9527, 64.4 mg/L for Corexit 9527, 65.4 mg/L for dispersed crude oil, and 190,000 mg/L for the water-accommodated fraction of Bass Strait crude oil. 

RIbo, J.M. and Kaiser, K.L.E. 1983. Effects of selected chemicals to photoluminescent bacteria and their correlations with acute and sub-lethal effects on other organisms. Chemosphere 12 1421-1442. 

A review of the lethal and sub-lethal effects of mercury on aquatic life... 

For lethal effects the effective concentration plotted is the LC50 value and for sub-lethal effects the effective concentration is the level of exposure that caused a 50% deviation from the control for the parameter measured, i.e., the EC50 value. 

Fish appear to be more sensitive to organic mercury compounds than to inorganic compounds, both lethal and sub-lethal effects being reported at exposure levels of 1.0 /Ag/L. The spawning behaviour of the minnow Pimephales promelas was inhibited by exposure for 42 days to 0.1 /Ag/L of methyl mercuric chloride, and at 0.2 ftg/L 90% died during the test period no effects were noted at exposures of 0.07 ftg/L (Mount 1974). 

A summary of the data presented in Tables I to IV is shown in Table V. This table shows the minimum concentrations of mercury compounds that have been shown to produce sub-lethal effects in an aquatic species, and also shows the range of concentrations within which 90% of the reported values fall. 

From Table V, it can be seen that inorganic compounds of mercury give rise to sub-lethal effects in the laboratory at concentrations > three ftg/L and lethal effects at concentrations > ten ftg/L. The corresponding values for organic mercury compounds are 0.1 fig/h and eight ftg/L. 

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