PsycbologicalReports, 1990, 66, 839-844. @ Psychological Reports 1990

LEAD AND CADMIUM LEVELS I N VIOLENT CRIMINALS ' R. 0. PIHL AND F. ERVIN Departments of Psychology and Psychiatry, McGill University Summary.-Two groups of violent incarcerated male criminals and 30 nonviolent criminals were compared for element content of hair by atomic absorption spectroscopy. Groups did not differ in age, socioeconomic status, or months institutionalized. The groups did differ significantly in lead and cadmium levels. The importance of cadmium in affecting reactivity to stimuli is discussed.

The neurotoxicological effects of lead poisoning are well known (Goyer & Chisholm, 1972), including acting as a precipitant of mental retardation (Chisholm, 1965; Moncrieff, Korunides, Clayton, Patrick, Renwick, & Rob-

erts, 1964). Effects of "nontoxic" levels, ~ a r t i c u l a r lamong ~ children, have drawn considerable interest. Whether measured via hair analysis (Pihl & Parkes, 1977), in dentine (Needleman, Gunnoe, Leviton, Reed, Paresie, Maher, & Barrett, 1979; Gilberg, Noren, Wahlstrom, & Rasmussen, 1982) or in blood (Bryce-Smith & Waldron, 1974), the greater the lead level the more learning problems (Pihl & Parkes, 1977), hyperactivity (David, Hoffman, Sverd, Clark, & Voeller, 1976), diminished intelligence (Needleman, et a/., 1979), and behavioral ~roblems(Pihl, Drake, & Vrana, 1980) have been reported. While controversy exists regarding the degree of decrement relative to lead level and methodological differences and concerns in these studies abound, evidence of impaired psychomotor functioning (Valcuikas, L a s , Fischbeing, Selikoff, Essinger, & Blumberg, 1978), attention span deficiency (De la Burde & Choate, 1975), and nonadaptive classroom behavior (Needleman, et al., 1979) have been described. "Nontoxic" levels of cadmium have also been implicated in learning and behavioral problems (Pihl & Parkes, 1977; Pihl, et al., 1980; Lester, Thatcher, & Monroe-Lord, 1982; Thatcher, Lester, McMaster, & Horst, 1982). I t has been suggested that cadmium and lead interact to produce increased aggression in school-age children (Marlowe, Stellern, Moon, & Errera, 1985). Although lead and cadmium have been shown to be positively related in blood and hair (Kubata, Legar, & Losee, 1968; Petering, Yenger, & Witherup, 1973; Pihl, et al., 1980), the aggression seen in these children may simply be a concomitant of hyperactivity which has also been related to lead levels. I t is important to assess the possible relationship between aggression and lead and cadmium levels in adults with specific aggressive patterns and histories. With the exception of one preliminary study with a small 'Address correspondence to R. 0. Pihl, Department of Psychology, 1205 Ave. Docteur Penfield, Montreal, Quibec H3A 1B1.



group of hospitalized adults and where element level was also related to age (Pihl, Ervin, Peletier, & Diekel, 1982), children have been the predominant focus in subtoxic lead and cadmium studies. The present study was designed to assess lead and cadmium levels in individuals selected for level of current aggressiveness and with violent and nonviolent histories.

METHOD Subjects Subjects were 49 male volunteer subjects between the ages of 19 and 48 yr. (mean of 34 yr.) who all were incarcerated in an institute for psychiatrically disturbed criminals. A ll were selected by ward staff for the study on the basis of amount of aggression exhibited on the ward. Potential subjects were classified as either high or low in aggressiveness by at least three ward personnel, and 100% agreement was required. In addition, the subjects were separated in terms of the type of crime committed. Thirty subjects with violent criminal histories, who were also aggressive o n the ward, comprised the violent group. Among this group there were 10 incidents of murder or attempted murder, 20 cases of assault, 9 instances of armed robbery, and 5 violent rapes. The 19 subjects who comprised the nonviolent group were uniformly seen as nonaggressive on the ward, and of the nine who had extensive criminal histories all involved incidents of nonviolent burglary. Procedure Lead and cadmium were measured for head-hair samples by atomic absorption spectroscopy. I n addition, nine other elements, calcium, magnesium, potassium, sodium, cobalt, copper, iron, manganese, and zinc were measured. No particular expectation existed relative to these additional elements. Approximately a tablespoon sample of hair was collected from each subject close to the scalp at the nape of the neck. Each subject had been instructed to wash his hair with a prescribed shampoo the evening before the sample was taken. Coded samples were analyzed blind according to the procedure of the Trace Element Laboratory at Case Western Reserve University (Strain, Paries, Flynn, & Hill, 1972). After the sample was obtained, subjects were also questioned as to their fathers' occupations if these were not present in the subjects' personal files so socioeconomic status could be estimated (Blishin & McRoberts, 1976). Lansdown, Shepherd, Clayton, Delves, Graham, and Turner (1974) have shown that blood lead level can correlate with socioeconomic status. History of drug use was noted for each subject.

RESULTS Chi-squared analyses were completed between the violent and nonviolent groups for the variables of age, fathers' socioeconomic status, months institutionalized, and home environment (urban or rural). Table 1 presents


84 1

mean values on these variables for the two groups. None of these control variables reached significance. Self-reported nonprescription drug use including cigarettes was not significantly different between the two groups, with the exception of an history of use of amphetamines. The violent group reported higher past use of this substance (F,,,, = 6.63, p < .02). TABLE




Nonviolent SD


Age, yr.

Socioeconomic Status Months Institutionalized Environment




27.6 4.1 25.2 1.2

7.8 1.3 32.9 0.4

28.7 4.1 18.6 1.3

5.4 1.3 20.3 0.4

A one-way analysis of variance for the two groups was performed for each of the 11 elements. Table 2 presents means and standard deviations of the elements by group and indicates that both cadmium (F,,,, = 19.49, p < .0005) and lead (F,,,, = 28.83, p < .0001) were significantly higher in the violent group. Pearson correlation of the elements showed that cadmium and lead were significantly correlated .33. I t should be noted that norms vary TABLE 2 SUMMARY OF MEANVALUES(PPM) FOREACH ELEMENT BY GROUP

Element Calcium











Magnesium Potassium Sodium Cadmium Cobalt Copper

Iron Lead Manganese Zinc

* p < .0005.

between laboratories, geographic area and with procedural differences. The obtained differences in Table 2 should therefore be viewed from a relative rather than an absolute perspective.

DISCUSSION The findings of the present investigation are in accord with those that



show a relationship between lead and cadmium levels and hyperactivity, behavioral problems and aggression in children. As the previous studies do not distinguish between hyperactivity with and without aggression, it is possible that aggression is in fact the behavior which was assessed. The multidimensional nature of hyperactivity with an aggressive component in some forms has been reported (Milich & Loney, 1977). A reasonable argument with regard to this finding of a relationship between lead and cadmium levels and aggressiveness is that it is fortuitous. I t is possible the relationship reflects differences in diet, economic status, living environment, drug use, etc. which may correlate both with cadmium and lead levels and with aggression. Some care was taken in the current investigation to assess variables known to affect both lead and cadmium levels, such as living environment, economic status and drug use, particularly cigarette smoking. As reported, only amphetamine use significantly differentiated the two groups. I t is, however, quite possible that a nonanticipated control variable accounts for the findings presented in this report. That other elements and their interaction may also be involved is illustrated by the study of Cromwell, Abadie, Stephens, and Kyler (1987). These authors found that, when violent criminals were compared with nonviolent criminals, the violent criminals showed different calcium/zinc, calcium/iron, copper/iron and iron/ manganese ratios. While substantial lead levels have been shown to affect sensorimotor and cognitive performance (Moore & Fleischman, 1775) and also it has been proposed that elements such as lead and cadmium may interact (Marlow, Jacobs, Moon, & Errera, 1984). Increasingly the role of cadmium is being implicated. The growing experimental evidence with animals supports the importance of effects of low cadmium levels on behaviour. These experiments show that animals given apparently nontoxic doses of cadmium display distinctive behaviours which can be seen as increasing the likelhood of aggressiveness. I t has been shown, for example, that rats exposed to cadmium display greater mouse killing than rats not similarly exposed (Arito, Sudo, & Suzuki, 1981). Further, rats exposed neonatally to cadmium show hyperactivity (Rastogi, Merali, & Singhal, 1977; Smith, Pihl, & Garber, 1982; Wong & Klassen, 1982). Saxe, Pihl, and Ervin (1789) have shown that repeated exposure to moderately low levels of orally administered cadmium in neonatal animals resulted in long-term changes in behaviour. These authors showed that postnatally cadmium-exposed rats were less reactive to a startling stimulus and spent more time in the inner circle of an open-field test. These results are interpreted as suggesting that cadmium administered postnatally serves to reduce fearful behaviour. An alternative explanation involving reduced arousal and increased stimulus-seeking behaviour would also be consistent with an increased propensity to aggression.



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Accepted April 2, 1970.

Lead and cadmium levels in violent criminals.

Two groups of violent incarcerated male criminals and 30 nonviolent criminals were compared for element content of hair by atomic absorption spectrosc...
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