Behaviour effects of lead

The investigation of the behavioural effects of lead in animals has drawn on all aspects of experimental psychology. Only studies employing rats or mice will be discussed here, although a large body of evidence is available for other animals (including fish, birds, sheep and primates). The behavioural effects of developmental lead exposure are summarized in Table 7. The doses and routes of administration for the studies outlined here are shown in Table 7. 

The investigation into the possible behavioural effects of lead at low doses has produced an enormous literature. All disciplines and approaches have been used, and the numerous different effects reported covered a whole range of neurobiological function. However, the approach to these studies was essentially the same as the original encephalopathy reports. A dose of lead was given that would produce an effect. Non-specific complications were noted, but rarely considered important. Few reports attempted to characterize the model of lead administration employed, and the myriad effects reported were based on a wide range of doses and durations of exposure. 

The hypothesis that the behavioural effects of lead are mediated via a lead-hippocampus interaction has received much attention. Indeed, the evidence for the possible involvement of the hippocampus in lead intoxication is quite large, although it is mainly of an indirect nature. From these results, it is possible to assume that lead may cause an alteration in hippocampal function. However, some of the reported behavioural effects of lead do not correlate well with a hippocampal dysfunction, therefore it is also possible to conclude that the behavioural effects of lead cause a wide variety... 

Bryce-Smith, D., Behavioural Effects of Lead and Other Heavy Metal Pollutants, Chem. Brit. 8 [1972] 240/3. 

Hansen ON, Trillingsgaard A, Beese I, et al A neuropsychological study of children with elevated dentine lead level assessment of the effect of lead in different socio-economic groups. Neurotoxicol Teratol 11 205-213, 1989 Haritos NP Chronic lead intoxication a report of 21 treated cases at Children s Hospital. Clinical Proceedings of the Children s Hospital 17 110-115,1961 Harvey PC, Hamlin MW, Kumar R Blood lead, behaviour and intelligence test performance in preschool children. Sci Total Environ 40 45-60, 1984 Hawk BA, Schroeder SR, Robinson G, et al Relation of lead and social factors to IQ of low-SES children a partial replication. American Journal of Mental Deficiency 91 178-183, 1986... 

Table 7 Behavioural effects of developmental lead exposure in rats and mice... 

A characteristic behaviour shown by rats is a class of exploratory activity known as spontaneous alternation. This is normally measured in a symmetrical T-, Y- or E-maze, and the animal is allowed to freely explore the apparatus on successive trials. The rat tends to distribute its responses in a non-random manner, visiting the most novel (least visited) arm on any given trial, and normal rats alternate spontaneously at a rate of 70-80%. The effect of lead on spontaneous alternation has been studied. 

Table 7b shows the large number of studies devoted to the effects of lead on learning (or more formally, conditioned behaviour), from simple learning through to the more complex responses to operant reinforcement. Learning... 

In summary, a review of the effects of lead on behaviour in the rat shows great diversity of findings. Only recently has adequate simulation of the exposure conditions found in young children been made. The measurement of blood lead makes correlation between studies easier, and is a useful index of exposure, helping to clarify the large number of regimens of lead administration that have been reported. There may be more accurate ways of assessing lead load, but blood lead measurements reflect a balance between convenience and accuracy. Other indices, such as dose or equivalence of effect may be less reliable and may make comparison between different studies difficult. 

The effect of lead on complex behaviour, such as social or aggressive behaviour, has been investigated in a relatively small number of studies. This category of experiment partly reproduces activity measurement in that the animal is observed for behavioural change with no experimental manipulation. There have been some reports of increased aggression and altered sexual behaviour these are doubtful. The reported changes to electroshock in lead-dosed animals appear more specific, but functionally uninterpretable. 

In the last 10 years, the neurotoxicological effects of lead have received intense attention, and some of the conclusions reached have been discussed here. Effects of lead have been seen at the behavioural, neurochemical and structural levels in the brain. As it appears that atmospheric lead dispersal will now begin to fall, the emphasis of research into the effects of lead is likely to change again. 

Gross-Selbeck, E. and Gross-Selbeck, M. (1980). Abiphasic effect of lead on operant behaviour of rats induced by different exposure. Toxicol. Lett. (Special Issue) 0, 128 (abstract P8)... 

The effects of lead on mental function and development in children including the foetus) will be discussed. The evidence presented indicts lead as a major cause of lower intellectual achievement in children as well as of a number of behavioural disorders. Because the human brain is the most complex and purposefully orderedform of matter known to us, and is the organ on which man depends for his unique position in the world, even the most marginal impairment in its function could be very highly geared to adverse consequences for human society. 

This review will aim to cover work on the possible neurological and behavioural effects of exposure to low levels of environmental lead which has been reported in the past 7 years. The review will be from a scientific viewpoint, thus it will not tackle the difficult problem of the policy implications which are attached to the findings, but will try to evaluate from a methodological and design viewpoint what is known as a result of the research carried out so far, and what we now need to know. The document is intended both as a description of the state of art, and as a guide to aid the interpretation and utilization of the results of existing research. 

McBride, W.G. (1984) Prospective study of health effects of lead in urban children. Paper presented at International Conference on Prospective Lead Studies, Cincinnati, Ohio, April McBride, W.G., Black, B.P. and English, B.J. (1982) Blood lead levels and behaviour of 400 preschool children. Med. ]. Australia, 2, 26-29 Mackie, A.C., Stephens, R., Townsend, A. and Waldron, H.A. (1977) Tooth lead levels in Birmingham children. Arch. Environ. Health, 32, 178-185 Mahaffey, K.R., Annest, J.L., Roberts, J. and Murphy, R.S. (1982) National estimates of blood lead levels United States, 1976-1980 association with selected demographic and socioeconomic factors. N. Engl ]. Med., 307, 149-159 Moore, M.R., Campbell, B.C., Meredith, P.A., Beattie, A.D., Goldberg, A. and Campbell, D. 

Yule> W. and Rutter, M. (1985) Effects of lead on children s behaviour and cognitive performance a critical review, in Mahaffey, K.R. (ed), Dietary and Environmental Lead Human Health Effects (Amsterdam Elsevier)... 

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