Occupational exposure to urban pollutants and urinary 5-hydroxy-3-indoleacetic acid.

Introduction

Serotonin (5-hydroxytriptamine, or 5-HT) is a heterocyclic amine that was first isolated by Esparmer and Vialli in 1937. Important depots in mammals were enterochromaffin cells in the gastrointestinal mucosa, serotonergic neurones of the brain, the pineal gland, and platelets. 5-HT is involved in a variety o[ physiological processes, including smooth muscle contraction, blood pressure regulation, body temperature regulation, pain sensitivity, mood control, sleep onset, and both peripheral and central nervous system neuro-transmission. It plays a major role in various psychiatric disorders, including schizophrenia (Breier, 1995), obesity (Bjorntorp, 1995: Wurtman & Wurtman, 1995), bulimia and anorexia nervosa (Kaye & Weltzin, 1991), alcoholism (Badawy, Morgan, & Thomas, 1993), obsessive-compulsive disorder (Jarry & Vaccarino, 1996), depression (Leonard, 1996; Owens & Nemeroff, 1994; Strickland et al., 2002), and impulsive violence and suicidal behavior (Linnoila & Virkkunnen, 1992; Nelson & Chiavegatto. 2001; Virkkunnen, Goldman, Nielsen, & Linnoila, 1995). The effects of 5-HT are felt most prominently in the cardiovascular system, with additional effects in the respiratory system and the intestine. Circlating 5-HT is metabolized to 5-hydroxy-3-indoleacetic acid (5-HIAA), which is excreted in the urine.

Studies on animals and human subjects have proposed that urban pollutants may cause a diminished 5-HT turnover. The agents are carbon monoxide (Muraoka, Hayakawa, Kagaya, Kojima, & Yamawaki, 1998). toluene (Arito, Tsuruta, Nakagaki & Tanaka, 1985; Hsieh, Sharma, Parker, & Coulombe. 1990), lead (Lasley, Greenland, Minnema & Michaelson, 1984) and noise (Fruhstorfer et al., 1985). By contrast, benzo[a]pyrene (Jayasekara, Sharma & Drown, 1992), benzene (Paradowski, Heimburger, Cohen, & Andrzejewski, 1984), and stirene (Husain, Srivastava, Mushtaq, & Seth, 1980) may cause an increase of 5-HT turnover.

The workers examined in this study were employees of the municipal police force of a large Italian city, for whom the authors had already studied the environmental and biological levels of some urban pollutants (Crebelli et al., 2001; Galati et al., 2001; Tomei et al., 2001; Verdina et al., 2001). Exposure dosage to benzene (for a mean of seven hours) was 10.7 [micro]g/[m.sup.3] for traffic police but about three times lower (3.6 [micro]g/[m.sup.3]) in controls (Crebelli et al., 2001; Tomei et al., 2001). Although unleaded gasoline had been introduced in Italy at the time of this study, a mixed regimen existed in Italy at the time of the study (use of both leaded and unleaded gasoline). The use of unleaded gasoline caused the increase of benzene in urban air.

In the period March-April 2001, the municipality of the city in question monitored concentrations of P[M.sub.10] in fixed stations located in districts with different intensities of traffic, registering mean monthly values respectively of 60 [micro]g/[m.sup.3], 45 [micro]g/[m.sup.3], and 30 [micro]g/[m.sup.3] in a municipal park (http:// www.comune.roma.it).

The purpose of the study reported here was to evaluate whether traffic police exposed to urban pollutants could be at risk for alterations of urinary 5-HIAA in 24 hours (5-HIAA[U]) compared with a control group.

Materials and Methods

The research was carried out on a working population of 395 municipal police employees. For admission to the study, all workers completed a questionnaire in the presence of a physician to identify, the main non-occupational confounding factors, which comprised the following points: sex; age; duration of working life; duties performed; weight; height; pharmacological therapies; cigarette-smoking habit (mean number of cigarettes smoked, duration of the habit in years); and daily intake of alcohol (wine, beer, and spirits).

To prevent the influence of confounding factors, the study excluded subjects who regularly made use of oral contraceptives (Mueck, Seeger, Petersen, Shultze-Wintrop & Wallwiener, 2001; Seeger, Ludtke, Graser, Wallwiener & Mueck, 2000), antidepressant drugs (Breier, 1995; Linnoila, Miller, Bartko, & Potter, 1984), and betablocker drugs (Neftel & Gautschi, 1986); subjects who had a body mass index (BMI Kg/[m.sup.2]) above 30 (Bjorntorp, 1995); and subjects who had a cigarette-smoking habit (Benwell, Balfour & Anderson, 1990). Subjects who mentioned habitual consumption of alcoholic spirits were not present in the study. Subjects who mentioned habitual wine/beer consumption above two glasses per day were excluded from the study (Rosenwasser, 2001).

The authors divided all the remaining subjects into traffic police and control subjects. The traffic police exposed to urban pollutants worked on parking control, control of passages, and control of crossroads or roads with heavy traffic. The subjects doing indoor activities such as administrative and bureaucratic duties, at a lesser level of exposure, were used as a control group. Traffic police and controls worked for seven hours a day at least five days a week.

Traffic police were compared with controls by sex, age, working life, and drinking habit (less than two glasses of wine or beer per day) (mean, SD. distribution) (Table 1). The study included 140 subjects: 70 traffic police (41 women and 29 men), and 70 controls (41 women and 29 men).

All the workers included in the study underwent chromatography-colorimetric assay (Shihabi & Wilson, 1982) for 5-HIAA(U): The normal values of the test were the ones normally applied in the authors' laboratory, from 2.0 to 10 mg per 24 hours for both sexes. The urine samples were collected over a period of 24 hours (6 a.m. to 6 a.m.) and kept in a refrigerator at -4[degrees]C until they were moved (by means of a container at the same temperature) to the laboratory. Urine samples were collected on a 24-hour cycle to avoid circadian-rhythm influence (Garvey, Noyes, Woodman, & Cook, 1994).

All the workers were given instructions about how to collect the urine and about foods (those rich in tyramine and tryptophan, such as avocados, bananas, coffee, plums, pineapple and pineapple juice, tomatoes, walnuts) and medicines (aspirin, corticotropin, acetaninophen, phenazetin) that were not to be taken for 72 hours before collection.

The laboratory did not know which samples came from the exposed group and which from the control group, although both physicians and technicians were aware that a study was in progress.

All of the subjects consented to have details of their personal information made available for the study. All declared they had been made aware that these data are classified as "sensitive information" and gave their consent to have the data treated in an anonymous and collective way, with scientific methods and for scientific purposes, in accordance with the principles of the Declaration of Helsinki.

Statistical Analysis

The statistical analysis of the data was based on calculation of the mean, standard deviation, distribution, range, and frequency values according to the nature of the single variables.

The differences between the means were compared with Student's t-test for the unpaired data. The frequencies of the single variables were compared with the Chi-square test and Yates's correction. The differences were considered significant when the p values were <.05. The statistical analysis was done with Solo-BMDP[TM] Statistical Software.

Results and Discussion

Mean 5-HIAA(U) levels were significantly lower in traffic police than in male controls (p = .025) (Table 1). Among females, mean 5-HIAA(U) levels also were significantly lower in traffic police than in controls (p = .027) (Table 1).

No traffic police or control subjects had 5-HIAA(U) values outside the laboratory's normal range. The distributions of the 5-HIAA(U) values in the exposed workers and controls are shown for males and females, respectively, in Figure 1 (p = .000) and Figure 2 (p = .004). Since subjects with the main confounding factors were excluded from the study, and the subjects investigated were matched by sex, age, and working life, the data suggest the possibility that occupational exposure to urban pollutants in traffic police can have an influence on 5-HT turnover and therefore on 5-HIAA(U)]excretion.

[FIGURE 1-2 OMITTED]

The significant differences between the means for exposed workers and controls suggest that they may be of some clinical relevance even when the mean is "numerically" normal.

The action mechanisms of chemical and physical agents that are present as urban pollutants and are able to modify 5-HIAA(U) levels are still uncertain. Studies on animals and human subjects have led to the hypothesis that exposure to chemical and physical agents could decrease (Arito et al., 1985; Fruhstorfer et al., 1985; Lasley et al., 1984; Muraoka et al., 1998) or increase (Jayasekara et al., 1992; Paradowski et al., 1984) serotonergic activity, probably in relation to the doses, modality, and time of exposure.

Effects of carbon monoxide (CO) exposure on 5-HT and 5-HIAA concentration in animals were evaluated by Muraoka and coauthors (1998). 5-HT concentration was significantly decreased in the frontal cortex, and 5-HIAA was increased in the frontal cortex, striatum, hypothalamus, hyppocampus, midbrain, and pons (Muraoka et al.).

In rats exposed to toluene inhalation, serotonin syndrome was found to arise; that study suggests that toluene inhalation may affect serotonergic function (Yamawaki, Segawa, & Sarai, 1982) according to Ladefoged and coauthors (1991). Repeated administration of toluene in rats was associated with lowered concentrations of 5-HT in the frontal cortex, hippocampus, and midbrain and of 5-HIAA in midbrain and hypothalamus; these alterations were associated with insomnia, hyperactivity, and hyperdipsia (Arito et al., 1985). Insomnia was found also in workers exposed to toluene vapor (Antti-Poika, 1982). Other authors showed an increase in brain 5-HT and 5-HIAA in animals exposed to toluene (Honma, Sudo, Miyagawa, Sato, & Hasegawa, 1983; Rea, Nash, Zabik, Born, & Kessler, 1984; Hsieh et al., 1990).

Exposure to styrene in rats produced a significant increase in brain 5-HT and caused a significant decrease in monoamine oxidase (MAO) activity (Husain, Srivastava, Mushtaq, & Seth, 1980).

Animals exposed to low doses of lead (Pb) had a significant 5-HIAA decrease in six of nine brain regions observed (Lasley et al., 1984). Urinary excretion of 5-HIAA was not influenced in rats and workers exposed to Pb (Ichiba & Tomokuni, 1987).

Jayasekara and co-authors (19t)2) found an increase of brain 5-HIAA in laboratory animals after injection of benzo[a]pyrene. Another study in rats exposed to benzo[a]pyrene showed an increase in cortex 5-HIAA (Stephanou, Konstandi, Pappas, & Marselos, 1998). These studies demonstrate that benzo[a]pyrene induces alterations in the serotonergic system throughout the brain.

A single injection of benzene produced a significant increase of 5-HIAA content in striatum but not in the hypothalamus (Paradowski et al., 1984).

In rats exposed to hydrocarbon fuels and solvents, alteration in serum 5-HIAA concentration was found (Rossi, Nordholm, Carpenter, Ritchie, & Malcomb, 2001). One mechanism of action that could lead to a decrease in 5-HIAA (U) excretion following exposure to urban pollutants might be inhibition by some chemical agents (such as CO, toluene, and styrene) of the principal enzymes responsible for the metabolism of serotonin (i.e., tryptophan hydroxylase, MAO A and MAO B) (Egashira, Takayama, Sakai, & Yamanaka, 2000; Husain et al., 1980; Pahwa & Kalra, 1993) even in the presence of other pollutants (such as benzene, benzo[a]pyrene) that could cause activation.

After noise exposure in human subjects, a decrease of serotonergic metabolites was found (Fruhstorfer et al., 1985).

Several studies suggest that 5-HT is an important component of the central network that provides adaptation to stress (Chaouloff, 1993; Flugge, 1995; Kirby; el al., 1997) by means of increase in 5-HT syntbesis/turnover (Berton, Aguerre, Sarrieau, Mormede, & Chaouloff, 1998; Chaouloff, Berton, & Mormede, 1999; Goldstein, Rasmusson, Bunney, & Roth, 1996). By contrast, Campmany, Pol, & Armario (1996) reported that brain 5-HT metabolism was less sensitive than adrenocorticotropic hormone (ACTH) to the process of habituation to a repeated stressor. In students, examination stress did not induce a significant alteration of urinary 5-HIAA (Frankenhaeuser, Lundberg, Rauste von Wright, von Wright, & Sedvall, 1986).

The authors' previous research has ascertained, through the compilation and elaboration of a questionnaire, a greater subjective stress and an increase in plasma ACTH levels in traffic police compared with a control group. Sources of stress for the traffic police may be relations with the public, exposure to episodes of criminality; and the need to maintain high levels of services in various contexts (Pancheri et al., 2002).

Conclusion

It might be supposed that there is an effect on serotonergic turnover and therefore on 5-HIAA(U) in employees of the city police exposed to chemical physical and psychosocial stressors present in living and working environments. If this theory, is valid, many occupational and environmental stressors could play a role in psychiatric pathologies for which the biological substrate is an alteration in 5-HT (Davis et al., 1988; Vandel et al., 1985).

The data suggest that the laboratory test used in this study, which together with examination of other biological parameters, could improve methods for early detection of occupational exposure to urban pollutants.

TABLE 1

Mean Age, Mean Working Life, Mean Values of [5-HIAA(U)] in Traffic
Police and Controls of Both Sexes

                     Male Workers (n = 58)     Female Workers (n = 82)

                    Traffic                    Traffic
                    Police       Controls       Police       Controls
                   (n = 29)      (n = 29)      (n = 41)      (n = 41)

Age
  Mean (SD)       44.6 (5.4)     45.5 (6)     38.6 (4.1)    38.4 (4.3)
  Range              35-57        34-54         33-48         32-49

Working life
    (years)
  Mean (SD)        10.4 (4)     10.2 (4.5)    6.8 (5.1)     6.7 (4.4)
  Range              2-23          4-21          1-25          1-23

5-HIAA(U)
    values (mg/
    24 hours)
  Mean (SD)       3.6 (1.5) *   4.6 (1.8)    3.1 (1.1) **   3.7 (1.3)
  Range               2-7          2-8           2-6           2-7

* p = .025 with respect to control workers.

** p = .027 with respect to control workers.

SD = standard deviation.

REFERENCES

Antti-Poika, M. (1982). Prognosis of symptoms in patients with diagnosed chronic organic solvent intoxication. International Archives of Occupational and Environmental Health, 51 (1), 81.

Arito, H., Tsuruta, H., Nakagaki, K., & Tanaka, S. (1985). Partial insomnia, hyperactivity and hyperdipsia induced by repeated administration of toluene in rats: Their relation to brain monoamine metabolism. Toxicology, 37(1-2), 99-110.

Badawy, A.A., Morgan, C.J., & Thomas, R. (1993). Tryptophan and 5-hydroxytryptamine metabolism in alcoholism. In P.V. Taberner & A.A. Badawy (Eds.), Advances in biomedical alcohol research (pp. 231-235). Oxford: Pergamon Press.

Benwell, M.E.M., Balfour, D.J.K., & Anderson, J.M. (1990). Smoking-associated changes in the serotonergic systems of discrete regions of human brain. Psychopharmacology (Berlin), 102(1), 68-72.

Berton, O., Aguerre, S., Sarrieau, A., Mormede, P., & Chaouloff, F. (1998). Differential effects of social stress on central serotonergic activity and emotional reactivity in Lewis and spontaneously hypertensive rats. Neuroscience, 82(1), 147-159.

Bjorntorp, P. (1995). Neuroendocrine abnormalities in human obesity. Metabolism, 44(Suppl. 2), 38-41.

Breier, A. (1995). Serotonin, schizophrenia, and antipsychotic drug action. Schizophrenia Research, 14(3), 187-202.

Campmany, L., Pol, O., & Armario, A. (1996). The effects of two chronic intermittent stressors on brain monoamines. Pharmaology, Biochemistry, and Behavior, 53(3): 517-523.

Chaouloff, F. (1993). Physiopharmacological interactions between stress hormones and central serotonergic systems. Brain Research Reviews, 18(1), 1-32.

Chaouloff, F., Berton, O., & Mormede, P. (1999). Serotonin and stress. Neuropsychopharmacology, 21(Suppl. 2), 28S-32S.

Crebelli, R., Tomei, E, Zijno, A., Ghittori, S., Imbriani, M., Gamberale, D., Martini, A., & Carere, A. (2001). Exposure to benzene in urban workers: Environmental and biological monitoring of traffic police in Rome. Occupational and Environmental Medicine, 58(3), 165-171.

Davis, J.M., Koslow, S.H., Gibbons, R.D., Maas, J.W., Bowden, C.L., Casper, R., Hanin, I., Javaid, J.I., Chang, S.S., & Stokes, P.E. (1988). Cerebrospinal fluid and urinary biogenic amines in depressed patients and healthy controls. Archives of General Psychiatry, 45, 705-717.

Egashira, T., Takayama, F., Sakai, K., & Yamanaka, Y. (2000). Styrene inhibits monoamine oxidase A, but not monoamine oxidase B in monkey brain mitochondria. Toxicology Letters, 117(1-2), 115-119.

Flugge, G. (1995). Dynamics of central nervous 5-HT1A-receptors under psychosocial stress. Journal of Neuroscience, 15(11), 7132-7140.

Frankenhaeuser, M., Lundberg, U., Rauste von Wright, M., von Wright, J., & Sedvall, G. (1986). Urinary monoamine metabolites as indices of mental stress in healthy males and females. Pharmacology, Biochemistry, and Behavior, 24(6), 1521-1525.

Fruhstorfer, B., Fruhstorfer, H., Grass, P., Milerski, H.G., Sturm, G., Wesemann, W., & Wiesel D. (1985). Daytime noise stress and subsequent night sleep: Interference with sleep patterns, endocrine and neurocrine functions. International Journal of Neuroscience, 26(3-4), 301-310.

Galati, R., Zijno, A., Crebelli, R., Falasca, G., Tomei, F., Iecher, F., Carta, P., & Verdina, A. (2001). Detection of antibodies to the benzo(a)pyrene did epoxide-DNA adducts in sera from individuals exposed to low doses of polycyclic aromatic hydrocarbons. Journal of Experimental & Clinical Cancer Research, 20(3), 359-364.

Garvey, M.J., Noyes, R., Jr., Woodman, C., & Cook, B. (1994). The reliability of urinary 5-HIAA levels. Neuropsychobiology, 29(4), 185-188.

Goldstein, L.E., Rasmusson, A.M., Bunney, B.S., & Roth, R.H. (1996). Role of the amygdala in the coordination of behavioral, neuroendocrine, and prefrontal cortical monoamine responses to psychological stress in the rat. The Journal of Neuroscience, 16(15), 4787-4798.

Honma, T., Sudo, A., Miyagawa, M., Sato, M., & Hasegawa, H. (1983). Significant changes in the amounts of neurotransmitter and related substances in rat brain induced by subacute exposure to low levels of toluene and xylene. Industrial Health, 21(3), 143-151.

Hsieh, G.C., Sharma, R.P., Parker, R.D., & Coulombe, R.A., Jr. (1990). Evaluation of toluene exposure via drinking water on levels of regional brain biogenic monoamines and their metabolite in CD-1 mice. Ecotoxicology and Environmental Safety, 20(2), 175-184.

Husain, R., Srivastava, S.P., Mushtaq, M., & Seth, P.K. (1980). Effect of styrene on levels of serotonin, noradrenaline, dopamine and activity of acetyl cholinesterase and monoamine oxidase in rat brain. Toxicology Letters, 7(1), 47-50.

Ichiba, M., & Tomokuni, K. (1987). Urinary excretion of 5-hydroxyindoleacetic acid, delta-aminolevunilic acid and coproporphyrin isomers in rats and men exposed to lead. Toxicology Letters, 38(1-2), 91-96.

Jarry, J.L., & Vaccarino, F.J. (1996). Eating disorders and obsessive-compulsive disorders: Neurochemical and phenomenological commonalities. Journal of Psychiatry & Neuroscience, 21(1), 36-48.

Jayasekara, S., Sharma, R.P., & Drown, D.B. (1992). Effects of benzo[a]pyrene on steady-state levels of biogenic amines and metabolizing enzymes in mouse brain regions. Ecotoxicology and Environmental Safety, 24(1), 1-12.

Kaye, W.H., & Weltzin, T.E. (1991). Serotonin activity in anorexia and bulimia nervosa: Relationship to the modulation of feeding and mood. The Journal of Clinical Psychiatry, 52(Suppl. 12), 41-48.

Kirby, L.G., Chou-Green, J.M., Davis, K., & Lucki, I. (1997). The effects of different Stressors on extracellular 5-hydroxytryptamine and 5-hydroxyindoleacetic acid. Brain Research, 760(1-2), 218-230.

Ladefoged, O., Strange, P, Moller, A., Lam, H.R., Ostregaard, G., Larsen, J.J., & Arlien-Soborg, P. (1991). Irreversible effects in rats of toluene (inhalation) exposure for six months. Pharmacology & Toxicology, 68(5), 384-390.

Lasley, M.S., Greenland, R.D., Minnema, D.J., & Michaelson, I.A. (1984). Influence of chronic inorganic lead exposure on regional dopamine and 5-hydroxytryptamine turnover in rat brain. Neurochemical Research, 9(12), 1675-1688.

Leonard, B.E. (1996). Serotonin receptors and their function in sleep, anxiety disorders, and depression. Psychotherapy and Psychosomatics, 65(2), 66-75.

Linnoila, M., Miller, T.L., Bartko, J., & Potter, W.Z. (1984). Five antidepressant treatments in depressed patients. Effects on urinary serotonin and 5-hydroxyindoleacetic acid output. Archives of General Psychiatry, 41(7), 688-692.

Linnoila, V.M., & Virkkunnen, M. (1992). Aggression, suicidality, and serotonin. The Journal of Clinical Psychiatry, 53(Suppl. 10), 46-51.

Mueck, A.O., Seeger, H., Petersen, G., Schultze-Wintrop, E., & Wallwiener, D. (2001). Effect of two oral contraceptives with different ethinyl estradiol and levonorgestrel concentrations on the urinary excretion of biochemical vasoactive markers. Contraception, 64(6), 357-362.

Muraoka, M., Hayakawa, H., Kagaya, A., Kojima, T., & Yamawaki, S. (1998). Effects of carbon monoxide exposure on serotonergic neuronal systems in rat brain. Life Sciences, 62(23), 2101-2108.

Neftel, K.A., & Gautschi, K. (1986). Atenolol and pindolol interfere with urinary 5-hydroxyindole-3-acetic acid. International Journal of Clinical Pharmacology, Therapy and Toxicology, 24(2), 58-59.

Nelson, R.J., & Chiavegatto, S. (2001). Molecular basis of aggression. Trends in Neurosciences, 24(12), 713-719.

Owens, M.J., & Nemeroff, C.B. (1994). Role of serotonin in pathophysiology of depression: Focus on the serotonin transporter. Clinical Chemistry, 40(2), 288-295.

Pahwa, R., & Kalra, J. (1993). A critical review of the neurotoxicity of styrene in humans. Veterinary and Human Toxicology, 35(6), 516-520.

Pancheri, P., Martini, A., Tarsitani, L., Rosati, M.V., Biondi, M., & Tomei, F. (2002). Assessment of subjective stress in the municipal police force of the city of Rome. Stress and Health, 18(3), 127-132

Paradowski, M., Heimburger, M., Cohen, Y., & Andrzejewski, S. (1984). The effects of a single dose and prolonged benzene administration on 5-hydroxytryptamine and 5-hydroxyindolacetic acid content in rat brain. Xenobiotica, 14(10), 781-784.

Rea, T.M., Nash, J.F., Zabik, J.E., Born, G.S., & Kessler, W.V. (1984). Effects of toluene inhalation on brain biogenic amines in the rat. Toxicology, 31(2), 143-150.

Rosenwasser, A.M. (2001). Alcohol, antidepressants, and circadian rhythms. Human and animal models. Alcohol Research & Health, 25(2), 126-135.

Rossi, J., 3rd, Nordholm, A.F., Carpenter, R.L., Ritchie, G.D., & Malcomb, W. (2001). Effects of repeated exposure of rats to JP-5 or JP-8 jet fuel vapor on neurobehavioral capacity and neurotransmitter levels. Journal of Toxicology and Environmental Health (Part A), 63(6), 397-428.

Seeger, H., Ludtke, R., Graser, T., Wallwiener, D., & Mueck, A.O. (2000). Effect of oral contraceptives on the urinary excretion of biochemical markers indicating vasoactive action. Journal of Clinical Pharmacy and Therapeutics, 25(3), 221-226.

Shihabi, Z.K., & Wilson E.L. (1982). Colorimetric assay of urinary 5-hydroxy-3-indoleacetic acid. Clinical Biochemistry, 15(2), 106-108.

Stephanou, P., Konstandi, M., Pappas, P., & Marselos, M. (1998). Alterations in central monoaminergic neurotransmission induced by polycyclic aromatic hydrocarbons in rats. European Journal of Drug Metabolism and Pharmacokinetics, 23(4), 475-481.

Strickland, P.L., Deakin, J.F., Percival, C., Dixon, J., Gater, R.A., & Goldberg, D.P. (2002). Bio-social origins of depression in the community. Interaction between social adversity, cortisol and serotonin neurotransmission. The British Journal of Psychiatry, 180(2), 168-173.

Tomei, F., Ghittori, S., Imbriani, M., Pavanello, S., Carere, A., Marcon, F., Martini, A., Baccolo, T.P., Tomao, E., Zijno, A., & Crebelli, R. (2001). Environmental and biological monitoring of traffic wardens from the city of Rome. Occupational Medicine (London), 51 (3), 198-203.

Vandel, S., Vandel, B., Bonib, B., Camejo, Z., Sandoz, M., Allers, G., & Volmat, R. (1985). Biological markers in depression. Monoamine metabolites in urine of depressed patients and normal subjects. Pharmacopsychiatry, 18(6), 347-350.

Verdina, A., Galati, R., Falasca, G., Ghittori, S., Imbriani, M., Tomei, F., Marcellini, L., Zijno, A., Del Vecchio, V., & Crebelli, R. (2001). Metabolic polymorphism and urinary biomarkers in subjects with low benzene exposure. Journal of Toxicology and Environmental Health (Part A), 64(8), 607-618.

Virkkunnen, M., Goldman, D., Nielsen, D.A., & Linnoila, M. (1995).

Wurtman, R.J., & Wurtman, J.J. (1995). Brain serotonin, carbohydrate-craving, obesity and depression. Obesity Research, 4(Suppl.4), 477S-480S.

Yamawaki, S., Segawa, T., & Sarai, K. (1982). Effects of acute and chronic toluene inhalation on behavior and (3H)-serotonin binding in rat. Life Sciences, 30(23), 1997-2002.

Corresponding author: Professor Francesco Tomei, Via Monte delle Gioie no. 13, 00199, Rome, Italy. E-mail: [e-mail].