Neurobehavioural effects

Unfortunately, there is no general agreement as to the threshold lead levels in blood that cause obvious central nervous system symptoms. Lead encephalopathy, a degenerative disease of the brain, is, however, unlikely to occur in adults with PbB 120 /xg (100 ml) L The evidence points to a lower threshold of 100 jUg (100 ml) for children [6]. 

Children are acknowledged to be more susceptible to lead poisoning for a wide variety of reasons, which include a greater intake and hence uptake of lead from the diet and the atmosphere per unit body weight, as well as the incomplete development of metabolic pathways and the blood-brain barrier [6]. Concern is therefore, now focused on the neurobehavioural effects of lead in children, in particular on the more subtle effects, which have become widely known as sub-clinical , although this term is strictly self-contradictory. These effects consist mainly of cognitive (mental) or sensory-motor integration (coordination) deficiencies. 

Subtle lead poisoning represents a particularly controversial area of research at present. Studies with similarly exposed groups have shown both positive and negative relationships between lead exposure and neurobehavioural effects. Many studies, however, reveal methodological faults and weaknesses, which limit the vaUdity of some of the conclusions. Nevertheless, the study, by Needleman and co-workers [23], is generally accepted as providing the most reliable information currently available [24]. As this is such an important study, it will be considered in some detail. 

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Studies of non-cancer effects in children have indicated neurodevelopmental delays and neurobehavioural effects, including neonatal hypotonia. In children in Seveso who were highly exposed to TCDD, small, transient increases in hepatic enzymes, total lymphocyte counts and subsets, complement activity, and non-permanent chlo-racne were observed. Also, an alteration of the sex ratio (excess female to male) was observed in children born to parents highly exposed to TCDD. 

Female Fischer 344 rats treated with a single oral dose (up to 5000 mg/kg bw) or with repeated doses (up to 1500 mg/kg bw per day for 14 days) of di(2-ethylhexyl) phthalate showed no neurobehavioural effects, as evaluated by functional observational battery and motor activity testing (Moser et al, 1995). 

Moser VC MacPhail RC (1989) Neurobehavioural effect of triadimefon, a triazole fungicide, in male and female rats. Neurotoxicol Teratol, 11(3) 285-293. 

Fatalities have been associated with acute or prolonged exposure to dichloromethane (Moskowitz Shapiro, 1952 Ku elova et al., 1975 Stewart Hake, 1976 Bonventre etal., 1977 Bakinson Jones, 1985 Manno etal., 1989). Temporary neurobehavioural effects have been reported after exposure to doses as low as 200 ppm [694 mg/m ] by some (Winnekke, 1974 Putz et al., 1976) but not by others (Gamberale et al., 1975). 

Farahat etal.. Neurobehaviour effects among workers occupationaDy exposed to oiganophosphorus pestiddes. Occupational and Environment j Medicine (2003) 60 279-286 http //oem.hmjjoumals.eom/cgi/reprint/60/4/279... 

Williamson AM, Teo RKC Neurobehavioural effects of occupational exposure to lead. 

Gamble JG Low-level hydrocarbon solvent exposure and neurobehavioural effects. Occup Med (Lond) 50 81-102, 2000... 

Cherry N, Venables H, Waldron HA British studies on the neuropsychological effects of solvent exposure. Scand J Work Environ Health 10 (suppl 1) 10-12, 1984 Cherry N, Hutchins H, Pace T, et al Neurobehavioural effects of repeated occupational exposure to toluene and paint solvents. British Journal of Industrial Medicine 42 291-300, 1985... 

Escalona E, Yanes L, Feo O, et al Neurobehavioral evaluation of Venezuelan workers exposed to organic solvent mixtures. AmJInd Med 27 15-27, 1995 Eskenazi B, Gaylord L, Bracken MB, et al In utero exposure to organic solvents and human neurodevelopment. Dev Med Child Neurol 30 492-501, 1988 Feldman RG, Ratner MH, Ptak T Chronic toxic encephalopathy in a painter exposed to mixed solvents. Environ Health Perspect 107 417 22,1999 Fidler AT, Baker EL, Letz RE Neurobehavioural effects of occupational exposure to organic solvents among construction painters. British Journal of Industrial Medicine 44 292-308, 1987... 

Skjodt T, Torfing KF, Teisen H Computed tomography in patients with dementia probably due to toxic encephalopathy. Acta Radiol 29 495-496,1988 Spurgeon A, Glass DC, Calvert IA, et al Investigation of dose related neurobehavioural effects in paintmakers exposed to low levels of solvents. Occup Environ Med 51 626-630, 1994... 

Workers in the chloralkaH industry were formerly occupationally exposed to mercury vapour. An increased frequency of intention tremors (time weighted average (TWA) of 0.026 mg/m ) was found in workers who inhaled mercury vapour for an average of 26 years. Neurobehavioural effects (motor speed, visual scanning, co-ordination and concentration) were affected in individuals with a TWA of 0.014 mg/m while workers exposed to an average of... 

Neurobehavioural effects of repeated occupational exposure to toluene and paint solvents. 

Winneke, G., Lilienthal, H. and Werner, W. (1982b) Task dependent neurobehavioural effects of lead in rats. Arch. Toxicol. (Suppl.), 5, 84-93... 

Winneke, G., Kraemer, U., Brockhaus, A., Ewers, U., Kujanek, G., Lechner, H. and Janke, W. (1983a) Neuropsychological studies in children with elevated tooth-lead concentrations. II. Extended study. Int. Arch. Occup. Environ. Health, 51, 231-252 Winneke, G., Lilienthal, H. and Zimmermann, U. (1983b) Neurobehavioural effects of lead and cadmium, in Hayes, A.W., Schnell, R.C. and Miya, T.S. (eds). Developments in the Science and Practice of Toxicology (Amsterdam Elsevier)... 

In addition, lead has been shown to have subcellular effects in the CNS at the level of mitochondrial function and protein synthesis. In particular, some work has indicated that delays seen in cortical synaptogenesis and metabolic maturation following prenatal lead exposure may well underlie the delayed development of exploratory and locomotor function seen in other studies of lead s neurobehavioural effects. Further studies on the correlation between human PbB values and lead-induced disruptions of tetrahydrobiopterin metabolism indicate that subsequent interference with neurotransmitter formation may be linked to small reductions in IQ scores. 

In the present paper we report on a cross-sectional smelter study of the neurobehavioural effects of lead, addressing many of the methodological issues which have been identified in earlier studies. 

In earlier publications (Needleman et al, 1979 Bellinger and Needleman, 1982), we called attention to four common experimental problems encountered in studying the neurobehavioural effects of low-Ievel lead exposure (1) use of weak markers of exposure (2) use of insensitive measures of outcome (3) inadequate attention to confounders and (4) ascertainment bias. Two of these factors, weak exposure markers and insensitive measures of outcome, tend to bias conclusions towards the null ascertainment bias and inadequate attention to confounders, on the other hand, may bias conclusions in either direction -towards or away from the null. 

Neurobehavioural Effects of Foetal Lead Exposure The First Year of Life... 

While current or longer-term health significance of these effects for all individuals cannot be precisely determined, results of studies of the early neurobehavioural effects of low-level foetal lead exposure should be seriously considered by public health officials when setting standards for human exposure. 

Neurobehavioural effects of fetal lead exposure the first year of life. (This volume). Ernhart, C.B., Wolf, A.W., Kennard, M.J., Erhard, P., Filipovich, H.F. and Sokol, R.J. (1986). Intrauterine exposure to low levels of lead the status of the neonate. Arch. Environ. Health, 41, 287-291... 

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