Negative effects of laboratory chemicals on the

HealthMED - Volume 4 / Number 3 / 2010

Negative effects of laboratory chemicals on the reproductive health Alicelebic Selma Institute of Histology and Embryology, School of Medicine, University of Sarajevo, Bosnia and Herzegovina

Abstract The presence of hazardous chemicals in laboratory workplaces has raised concerns about their potential negative effects on fertility, pregnancy outcomes and birth defects in offspring. Occupational exposure to certain laboratory chemicals may directly affect the outcome of pregnancy, such as spontaneous abortion, stillbirth, pre-term birth, small-for-gestational age and birth weight and may also interact with fetal development, resulting in health effects in the offspring that range from congenital birth defects, neurobehavioral disorders at young age and even cancer in older age. In general, the reproductive toxins are hazardous chemicals which can affect the reproductive health before or after conception by chromosomal damage (mutagen) and by many different negative effects on fetuses (teratogen). These chemicals can seriously affect a developing embryo or fetus because the course of human development from conception to adulthood is extremely complex. Because of the complexity, there are numerous opportunities for “things to go wrong.” Between conception (the union of sperm and egg) and birth, human life advances from a single-cell zygote to an infant capable of living outside the womb. During this period, complex and rapid changes are normal, from the molecular level through all the biochemical and physical processes that determine the course of development. Cell division, migration, differentiation and apoptosis all must occur in the correct sequence in the correct spatial orientation, coordinated through a large number of control and signaling systems. Because of the complexity and speed of development and the high rate of growth through the prenatal period, this stage of development has a special set of vul-

nerabilities to environmental exposures that are not seen at any other time. It is essential that laboratory workers are guaranteed and provided with the maximum protection to prevent adverse reproductive health consequences. A timely recognition of the impact of hazardous agents, elimination of exposures in the workplace and education of laboratory workers are very important in this direction. Key words: laboratory chemicals, reproductive health, prenatal development Introduction Today many talk about the impact of various factors on health. Mode, working conditions and working and living environment are closely linked and can cause various acute and chronic damages to certain organs and organic systems and the organism as a whole. Reproductive system is more sensitive than the other organ systems. Reproductive health, in the broadest sens, the possibility that people have a normal, healthy offspring, can be damaged in many ways. The factors that have negative impact on the reproductive health may act and be expressed before conception, during intrauterine fetal development and after the birth of a new individue, during its postnatal life. Prior to conception, the menstrual cycle can be disturbed in females and fertility as well as sexual potency in males, which can lead to infertility or reduced fertility of a couple. Genetic damage in male and female sex cells can be transmitted to the offspring with the result of disease or developmental disorders, but can also lead to stillbirths and abortion. Damages during intrauterine development occur by transmission of hasardous agents through placenta from mother’s body to

Journal of Society for development in new net environment in B&H

643


offspring (eg drugs, chemicals, viruses) or by the direct action on the offspring (e.g. ionizing radiation) and can lead to stillbirth, spontaneous abortion and, if the offspring survives, to different diseases and congenital anomalies of the fetus. Toxic factors can be transmitted to the baby through breast milk or brought home on the parents working clothes. The main characteristics of prenatal development The effects of the environmental hasardous factors mostly depend on the developmental stage in which they operate and, in order to preserve reproductive health, essential knowledge of basic stages and characteristics of development is necessary. Individual human development begins at conception or fertilization, the process during which a male gamete or sperm (spermatozoon) unites with a female gamete or oocyte (ovum). Sexual cells, gametes, start to develop during fetal life, even though they do not mature until puberty. Toxic substances from the environment can damage germ cells and can so jeopardize fertility of an adult individual or interferre with its offspring health. The course of human development from conception to adulthood is extremely complex. A huge number of biochemical, physical and organisational processes must be precisely coordinated to assure proper development, maintain health and avoid disease. Because of the complexity, there are numerous opportunities for “things to go wrong”. To have the knowledge of the crucial stages in human development, from the moment of conception, and even those processes that precede it is necessary for a better understanding of the important moments for the occurrence of disturbances of normal development under the influence of harmful effects from the environment and for the establishment and promotion of strategic plans of protection from exposure to the harmful effects of these adverse environmental factors. The human development course is divided into two periods – the prenatal and the postnatal. The prenatal period occurs during pregnancy and includes the preembrional, the embrional and the 644

fetal period, and the postnatal period occurs after birth and includes the period of childhood and adolescence. During the period from conception to birth the new organism develops itself from a single cell called zygote to a newborn capable of living outside the mothers body. Regarding the complexity and speed of development and growth of the prenatal period, it is the most vulnerable of the developmental periods. All the numerous different processes, that properly coordinate in space and time, are based on the cell’s function and their changes. Some of the most incredible phenomenons is that from the one cell, zygote, develop more than 200 morphologically and functionally different cells. These basic developmental processes occur at the same time and intermingle each other. They are determined by genetic potential, environmental factors and regulatory factors (hormons, growth factors, cytokines, ions). One trillion cells, contained in the adult human organism, originate from the one cell, zygote, by the process of proliferation. Rapid cell division is the primary driver of development and that is why embrional cells have a very short cell cycle, generally. A shorter cell cycle, implying more rapid metabolic and control processes, generally makes cells more vulnerable to possible toxic effects. Fertilized oocyte, of 0.0015 mg and invisible by the naked eye, develops by prenatal growth to a newborn of about 3.200g weight and about 50cm in length. Characteristics of cell growth are doubling of the DNA, synthesis of specific proteins and other essential factors. Growth is regulated by genetic factors, the concentration of nutrients and oxygen, and regulatory mechanisms that involve a numerous growth and neuroendocrine factors. Induction is a process during which a group of cells through signaling molecules influence the second group of cells to differentiate into morphologically and functionally specific types of cells. The diversity of the cells is achieved by differentiation. They are different allthough they have the same genome, due to different expression activity of individual genes. Cell migration implies the movement of the whole cell or of its parts. Cells recognize each other, assemble, shift or move away by specific molecules. An important developmental process that allows the formation of tissues and



organs is apoptosis, the programmed cell death. The process is regulated by genes and takes place under the influence of internal and external factors that lead to cell death. Extraordinary complexity of all these developmental processes provides a wide range of possibilities for adverse impacts to influence and to disturb the formation. Speed and diverse nature of processes that occur during critical developmental periods explain their particular sensitivity. Prenatal development is commonly divided into three periods: preembryonic - the first two weeks after fertilization, embryonic - from 3rd to 8th week and fetal - from 9th week to the birth. In the first two weeks of development, during the preembryonic period, zygote divides many times, implants in the uterus wall and moulds in a simple embryo. Exposure to harmful factors in this period usually leads to death of the embryo, and lethal harmful effects result in spontaneous abortion. To determine that there existed a pregnancy is possible only with biochemical tests, for example, a positive pregnancy test. Three germ layers develop during embryonic period: ectoderm, endoderm and mesoderm. By their differentiation, through the processes of histogenesis, morphogenesis and organogenesis, develop the body cavities, the nerve tube, all organs and organ systems and body shapes. Histogenesis is the process of creating a tissue during which certain cells differentiate into morphologically distinct cells of epithelial, connective, muscle and nervous tissue and produce an appropriate extracellular matrix. Morphogenesis is a series of processes that involve coordinated creation of

internal organs with the precise plan of their spatial organization and the formation of the external appearance of the body. Organogenesis is the process of morphological and functional development of organs. Embryonic period is the most sensitive period of development during which organs are the most sensitive just at the time of their intensive development (Table 1). During the fetal period grows the fetal body mass occurs, but also fine morphologic, functional and biochemical processes that lead to the establishment of the almost complete structure and function of organs and their training for the function outside the mother’s body after the birth. In this period, decreases gradually the sensitivity of the fetus. Factors that damage reproductive health Many chemical substances (for example, pesticides, gases, metals), different physical factors (radiation, vibration, atmospheric pressure) and biological agents (viruses, bacteria, fungi, parasites) can significantly affect conception, pregnancy course and outcome and can damage reproductive health of people and their ability to have normal, healthy offspring, but for the reproductive health it is particularly important to have the knowledge of mutagens and teratogens. Mutagens are physical and chemical agents that lead to structural changes in genes, mutations. When these changes occur in the somatic cells of an organism, they remain there only as a change in that particular body and can not be transmitted

Table 1. Critical periods in some organs prenatal development Body System

Especially Sensitive

Development up to …

Central nervous system/Brain Heart Upper limbs Eyes Lower limbs Teeth Palate External genitalia Ears

4 to 8 weeks 5th to 9th weeks 6th to 10th weeks 6th to 10 weeks 6th to 10th weeks 9th to 11th weeks 9th to 11th weeks 9th to 11th weeks 6th to 11th weeks

Postnatal, through to adulthood 12th week 12th week Term 12th week Term 16th week Term 13th week

th


th

645


further to the offspring, whereas mutations that occur in germ cells are hereditary and are transmitted from generation to generation. The most famous physical mutagen is ionizing radiation (gamma and x-rays), while the chemical known mutagens are arsenic, ethidium bromide and alkylating agents (e.g., dimethyl sulfate). Teratogens are biological, chemical and physical agents that interfere with the normal embryonic development and thus lead to congenital malformations or fetal death. Teratogens differ from mutagens in the way that there must be present a developing fetus. Damage of the fetus (embryo) is most likely to occur early in pregnancy, during the first 8 - 10 weeks. Teratogens may produce

congenital malformations or death of the fetus without inducing damage to the pregnant woman. Chemicals with proven teratogenic effects or generally adverse effects on reproductive health are dibromochloropropane, lead, ethylene oxide, antimony, carbon disulfide, polychlorinated biphenols (PCBs), nitrous oxide, formaldehyde, ethylene dibromide(1). Adverse effects before and during conception Chemicals can affect the organism before it was conceived by effecting its germ cells. Germ cell development starts before birth and continu-

Table 2. Reproductive health damages of occupational exposure to chemicals Chemical agents Lead Mercury Organic solvents Tetrachloroethylene Glycol ethers Dibromopropane Ethylene oxide Anaesthetic gases Antineoplastic drugs

Pregnancy outcomes (maternal exposure) Low birth weight Spontaneous abortion Spontaneous abortion Spontaneous abortion Spontaneous abortion Menstrual disturbances, spontaneous abortion Pre-term birth, spontaneous abortion Spontaneous abortion Spontaneous abortion

Birth defects (maternal exposure) Neural tube defects

Cleft lip/palate Neural tube defects

Reduced semen quality Reduced semen quality

Cleft lip/palate

Reduced sperm count Azoospermia

Pesticides Ethylenedibromide

Semen quality (paternal exposure) Reduced sperm count

Neural tube defects, cleft lip/palate

Carbon sulfide

Reduced quantity and quality Reduced quantity and quality

Table 3. Disorders of men and women fertility occurred after chemicals exposure in workplace Chemical agents Lead Mercury Toluene Aliphatic hydrocarbons Aromatic hydrocarbons Tetrachloroethylene Glycol ethers Ethylene oxide Anaesthetic gases Pesticides

646

Maternal exposure + + + + + + + + + +

Paternal exposure +

+

+



es almost during the whole individual life. During this long period there are many possibilities to damage very sensitive germ cells. Therefore, the effects of harmful factors on them can lead to infertility or reduced fertility of a man or a woman. Thus, dibromochloropropane, used as a pesticide, fumigant, and nematocide leads to azoospermia and infertility of workers who use it (2,3). Decreased fertility was found in women whose mothers smoked cigarettes during pregnancy (4). Tables 2. and 3. show a negative impact on fertility and reproductive health damages occurred after peoples exposure to chemicals in the workplace (5). It is known that many factors from the environment can lead to such damage of germ cells that result in an increased incidence of malignancies, particularly leukemia, in the offspring of exposed persons (6-8). The connections between malignant diseases of the offspring whose fathers were exposed to benzene and various other harmful components are summarized on Table 4. A connection between the appearance of malignant diseases in the offspring of women who were exposed to various harmful factors in the workplace before conception (6,7,9) or both before and after conception (10) is found. Data from

the literature is shown in Table 5. Researches on animals clearly confirm that the exposure to harmful factors in the prenatal period can damage their future reproductive function in adult period. For example, prenatal exposure to chemicals with a high content of chlorine (2,3,7,8-tetrachlorodibenzo-p-dioxin and polychlorinated biphenol-169) was associated with reduced sperm production in rats (11,12) even after a single dose (13). The toxicity of lead, hexachlorobenzene, cyclophosphamide, and many other chemicals was also proven in the experimental animal ovaries (14-18). Experiments on animals confirm the observation in humans that germ cell exposure to harmful factors at work during their development increases the risk for the occurrence of malignant disease in their offspring, as well (19). Genetic studies suggest possible mechanisms that lead to the emergence of these consequences. Thus, it was observed that smoking and exposure to pesticides and products of combustion increases the occurrence of sperm aneuploidy (20,21) and chemical changes of sperm DNA which cause mutations by acting on fertility and heal-

Table 4. Association Between Preconception Exposures in Men and Cancer in Offspring Exposure

Dose to Father

Exposure Period

Benzene6 Diagnostic X-rays7 Ionizing

Not quantified Not quantified

Preconception Preconception

Cancer That Developed in Child Leukemia Leukemia

> 100 mSv

6 months prior to conception

Leukemia/non-Hodgkin’s

Lifetime preconception 6 months prior to conception Preconception Before birth Preconception

lymphoma Leukemia Leukemia Acute lymphoblastic leukemia Hepatoblastoma Leukemia

Radiation7,8 Metals6 Wood dust7

(milliSievert) > 100 mSv > 10 mSv 1-5 mSv Not quantified Not quantified

Table 5. Association Between Preconception Exposures in Women and Cancer in Offspring Exposure

Dose to Mother

Exposure Period

Food industry7

Not quantified

Preconception or prenatal

Cancer That Developed in Child Leukemia/non-Hodgkin’s lymphoma

Not quantified Not quantified

Preconception or prenatal Preconception

Hepatoblastoma Leukemia/non-Hodgkin’s lymphoma

Metal dusts, petroleum products, paints, pigments6 Radiation9


647


th of the offspring (22). DNA can also be altered by toxic activity during preconceptional period in female germ cells, for example, alcohol leads to disruption of chromosome duplication, resulting in aneuploid embryos (23). It is known that different effects of various environmental factors are possible during conception, or shortly after conception. Increased number of spontaneous abortions and congenital anomalies has been noted in populations in which fathers were exposed to anesthetic gases, lead, mercury, organic solvents, pesticides, marijuana and tobacco (24-29). Preterm birth and lower birth weight could be associated with fathers’ occupational exposure to lead, pesticides and organic solvents (27,30-32). Even four to five years after mother’s exposure to polychlorinated biphenyls in food, these substances are transferred through the placenta from the mother’s body to the child and cause the reduction of its birth weight (33). Also, lead stored in bone tissue of women after previous exposure, may be mobilized and transferred during pregnancy through blood and placenta to the offspring and may damage it (34,35). Adverse effects during prenatal development During early embryonic development a huge number of different genes are permanently activated and inactivated in a specific order which provides many opportunities for harmful factors to act. Today, it is considered that the harmful effects of environmental factors on the gene are “responsible” for the emergence of one fourth to one half of all developmental disorders (36). Also, it has been proven that ionizing radiation and mercury during the prenatal development can disturb the normal migration of neurons and thus lead to developmental disorders of nervous system (37). The normal developmental process of gradual differentiation of undifferentiated cells to those with very specific and complex shapes and functions is under the control of processes of signal transduction inside and between cells. This is another in a series of sensitive points during the development in which may manifest toxic effects of various adverse effects from the environment and it is well known that undifferentiated cells are significantly 648

more vulnerable than differentiated cells. Chemicals which are proven to damage the specific types of undifferentiated cells are ethanol (38), manganese (39), nicotine (40) and dioxin (41). Harmful effects of environmental factors during prenatal development can lead to early embryonic death, congenital malformations, slowed fetal growth, fetal death during late fetal development, complications of pregnancy and premature birth. Early embryonic death which is clinically manifested as a spontaneous abortion can be caused by a wide range of different harmful factors from the environment. It was found that excessive pregnant women’s intake of coffee and smoking increase risk of miscarriage (42,43). Increased number of spontaneous abortions was noted in pregnant women who were exposed to the harmful effects of cytostatics, organic solvents and pesticides in the workplace (25, 44-47). Exposure to organic solvents in the workplace before or during pregnancy leads to an increased risk of congenital malformations of the fetus (48) but leads also to an increased risk of preeclampsia in later stages of pregnancy (49). Numerous studies suggest an association between smoking during pregnancy and fetal intrauterine growth retardation as well as early child birth (50) but, paradoxically, it appears that smoking reduces the risk of preeclampsia (51). Most of the damages that occur in the later stages of prenatal development under the influence of harmful factors from the environment are expressed after birth in the form of functional disorders of organs and organic body systems, but not in the form of malformations or intrauterine growth retardation (52). Pathological processes that lead to these disorders begin to act at the time of exposure, but their consequences are not evident until the child is born. Thus, exposure of the fetus to neurotoxins such as lead, mercury and polychlorinated biphenyls, from the middle to the end of prenatal development, is associated with behavioral disorders that appear later in child’s life (53-55). Researches on animals and in humans clearly indicate the existence of the delayed effects of exposure to various harmful factors from the environment that occur during early development. However, detection and recording of latent and long-term negative impact on general health, including the reproductive health, in the broadest sense, is extremely



difficult and it is necessary to do an extensive and long-term study in the future of a huge number of factors on a large population sample. Acknowledgement Invited plenary lecture presented at the 2nd Congress of Association of Laboratory and Sanitary Technicians in Bosnia and Herzegovina with International Participation, Neum, May, 13-17, 2009. References 1. Chemical Classification & Safety Signs. http://staff. tuhsd.k12.az.us/gfoster/standard/nfpa.htm

study. BMJ 1997;315:1181. 10. McKinney PA, Juszczak E, Findlay E, et al. Preand perinatal risk factors for childhood leukemia and other malignancies: a Scottish case control study. Br J Cancer 1999; 80:1844-51. 11. Gray LE JR. Xenoendocrine disrupters: laboratory studies on male reproductive effects. Toxicol Lett 1998; 102-103:331-3. 12. Loeffler IK, Peterson RE. Interactive effects of TCDD and p,p¢-DDE on male reproductive tract development in in utero and lactationally exposed rats. Toxicol Appl Pharmacol 1999;154:28-39. 13. Gray LE JR, Ostby JS, Kelce WR. A dose-response analysis of the reproductive effects of a single gestational dose of 2,3,7,8-tetrachlorodibenzo-pdioxin in male Long Evans Hooded rat offspring. Toxicol Appl Pharmacol 1997; 146:11-20.

2. Goldsmith JR. Dibromochloropropane: epidemiological findings and current questions. Ann N Y Acad Sci 1997; 837:300-6.

14. Doerr JK, Hollis EA, Sipes IG. Species difference in the ovarian toxicity of 1,3-butadiene epoxides in B6C3F1 mice and Sprague-Dawley rats. Toxicology 1996;113:128-36.

3. Potashnik G, Porath A: Dibromochloropropane (DBCP): a 17-year reassessment of testicular function and reproductive performance. J Occup Environ Med 37:1287-92,1995.

15. Doerr JK, Hooser SB, Smith BJ, Sipes IG. Ovarian toxicity of 4-vinylcyclohexene and related olefins in B6C3F1 mice: role of diexpoxides. Chem Res Toxicol 1995;8:963-9.

4. Weinberg CR, Wilcox AJ, Baird DD. Reduced fecundability in women with prenatal exposure to cigarette smoking. Am J Epidemiol 1989; 129:10728.

16. Foster WG, Pentick JA, McMahon A, Lecavalier PR. Ovarian toxicity of hexachlorobenzene in the superovulated female rat. J Biochem Toxicol 1992;7:1-4.

5. Burdorf A, Figa-Talamanca I, Jensen TK, Thulstrup AM. Effects of occupational exposure on the reproductive system: core evidence and practical implications. Occup Med (Lond) 2006;56:516-520. 6. Buckley JD, Robison LL, Swotinsky R, et al. Occupational exposures of parents of children with acute nonlymphocytic leukemia: a report from the Childrens Cancer Study Group. Cancer Res 1989;

49(14):4030-7.

7. McKinney PA, Alexander FE, Cartwright RA, Parker L. Parental occupations of children with leukemia in Cumbria, north Humberside, and Gateshead. BMJ 1991; 302:681. 8. Roman E, Doyle P, Maconochie N, et al. Cancer in children of nuclear industry employees: report on children aged under 25 years from nuclear industry family study. BMJ 1999; 318:1443. 9. Draper GJ, Little MP, Sorahan T, et al. Cancer in offspring of radiation workers: a record linkage

17. Junaid M, Chowdhuri DK, Narayan R, Shanker R, Saxena DK. Lead-induced changes in ovarian follicular development and maturation in mice. J Toxicol Environ Health 1997;50:31-40. 18. Plowchalk DR, Mattison DR. Reproductive toxicity of cyclophosphamide of the C57BL/6N mouse: 1. Effects on ovarian structure and function. Reprod Toxicol 1992; 6:411-12. 19. Anderson LM, Diwan BA, Fear NT, Roman E. Critical windows of exposures for children’s health: cancer in human epidemiological studies and neoplasms in experimental animal models. Environ Health Perspect 2000;108(Suppl 3):573. 20. Harkonen K, Viitanen T, Larsen SB, Bonde JP, Lahdetie J. Aneuploidy in sperm and exposure to fungicides and lifestyle factors. Environ Mol Mutagen 1999;34:39-46. 21. Padungtod C, Hassold TJ, Millie E, et al. Sperm aneuploidy among Chinese pesticide factory workers: scoring by the FISH method. Am J INd Med


649


1999; 36:230-8. 22. Zenzes MT, Bielecki R, Reed TE. Detection of benzo[a]pyrene diol epoxide-DNA adducts in sperm of men exposed to cigarette smoke. Fertil Steril 1999;72:330-5. 23. Kaufman MH. The teratogenic effects of alcohol following exposure during pregnancy, and its influence on the chromosome constitution of the preovulatory egg. Alcohol 1997;32:113-28. 24. Antilla A, Sallmen M. Effects of parental occupational exposure to lead and other metals on spontaneous abortion. J Occup Environ Med 1995;37:915-21. 25. Arbuckle TE, Sever LE. Pesticide exposures and fetal death: a review of the epidemiologic literature. Crit Rev Toxicol 1998;28:229-70. 26. Cohen EN, Gift HC, Brown BW, et al. Occupational disease in industry and chronic exposure to trace anesthetic gases. J Am Dent Assoc 1980;101:21-31. 27. Kristensen P, Irgens LM, Daltveit AK, Andersen A. Perinatal outcome among children of men exposed to lead and organic solvents in the printing industry. Am J Epidemiol 1993;137:134-44. 28. Olshan AF, Faustman EM. Male-mediated developmental toxicity. Annu Rev Publ Health 1993;14:159-81. 29. Taskinen H, Antilla A, Lindbohm ML, Sallmen M, Hemminki K. Spontaneous abortions and congenital malformations among the wives of men occupationally exposed to organic solvents. Scand J Work Environ Health 1989;15:345-52. 30. Lin S, Hwang SA, Marshall EG, Marion D. Does paternal occupational lead exposure increase the risk of low birth weight or prematurity? Am J Epidemiol 1998;148:173-81. 31. Min YI, Correa-Vilasenor A, Stewart PA. Parental occupational lead exposure and low birth weight. Am J Ind Med 1996;30:569-78. 32. Savitz DA, Arbuckle T, Kaczor D, Curtis KM. Male pesticide exposure and pregnancy outcome. Am J Epidemiol 1997; 146:1025-36. 33. Lucier GW, Nelson KG, Everson RB, et al. Placental markers of human exposure to polychlorinated biphenyls and polychlorinated dibenzofurans. Environ Health Perspect 1987;76:79-87. 34. Gulson BL, Jameson CW, Mahaffey KR, et al. Pre-

650

gnancy increases mobilization of lead from maternal skeleton. J Lab Clin Med 1997;130(1):56-62. 35. Han S, Pfizenmaier DH, Garcia E, et al. Effects of lead exposure before pregnancy and dietary calcium during pregnancy n fetal development and lead accumulation. Environ Health Perspect 2000;108(6):527-31. 36. NRC: National Research Council. Scientific Frontiers in Developmental Toxicology and Risk Assessment. Washington D.C., National Academy Press, 2000, pp.88-153. 37. Rodier PM. Developing brain as a target of toxicity. Environ Health Perspect 1995;103(Suppl 6):73-6. 38. Mullikin-Kilpatrick D, Mehta ND, Hildebrandt JD, Triestman SN. Bi is involved in ethanol inhibition of L-type calcium channels in undifferentiated but not differentiated PC-12 cells. Mol Pharmacol 1995; 47:997-1005. 39. DiLorenzo D, Ferrari F, Agrati P, et al. Manganese effects on the human neuroblastoma cell line SK-ER3. Toxicol Appl Pharmacol 1996; 140:517. 40. Berger F, Gage FH, Vijayaraghavan S. Nicotinic receptor-induced apoptotic cell death of hippocampal progenitor cells. J neurosci 1998; 18:6871-81. 41. Murante FG, Gasiewicz TA. Hematopoietic progenitor cells are sensitive targets of 2,3,7,8-tetrachlorodibenzo-p-dioxin in C57BL/6J mice. Toxicol Sci 2000; 54:374-83. 42. Infante-Rivard C, Fernandez A, Gauthier R, David M, Rivard GE. Fetal loss associated with caffeine intake before and during pregnancy. JAMA 1993;270:2940-3. 43. Ness RB, Grisso JA, Hirschinger N, et al. Cocaine and tobacco use and the risk of spontaneous abortion. N Engl J Med 1999;340:333-9. 44. Lindbohm ML, Taskinen H, Sallmen M, et al. Spontaneous abortions among women exposed to organic solvents. Am J Ind Med 1990; 17:449463. 45. Lipscomb JA, Fenster L, Wrensch M, et al. Pregnancy outcomes in women potentially exposed to occupational solvents and women working in the electronics industry. J Occup Med 1991;33:597604. 46. Taskinen H, Kyyronen P, Hemminki K, et al. La-



boratory work and pregnancy outcome. J Occup Environ Med 1994; 36:311-319. 47. Valanis B, Vollmer WM, Steele P. Occupational exposure to antineoplastic agents: self-reported miscarriages and stillbirths among nurses and pharmacists. J Occup Environ Med 1999;41:6328. 48. Khattak S, K-Moghtader G, McMartin K, et al. Pregnancy outcome following gestational exposure to organic solvents: A prospective controlled study. JAMA 1999;281:1106-1109. 49. Hewitt JB, Tellier L. Risk of adverse outcomes in pregnant women exposed to solvents. J Obstet Gynecol Neonatal Nurs 1998;27:505-31. 50. Sprauve ME, Lindsay MK, Drews-Botsch CD, Graves W. Racial patterns in the effects of tobacco use on fetal growth. Am J Obstet Gynecol 1999;181:S22-7. 51. Zhang J, Klebanoff MA, Levine RJ, Puri M, Moyer P. The puzzling association between smoking and hypertension during pregnancy. Am J Obstet Gynecol 1999; 181:1407-13. 52. Rice D, Barone S Jr. Critical periods of vulnerability for the developing nervous system: evidence from human and animal models. Environ Health Perspect 2000; 108(Suppl 3):511-33. 53. Grandjean P, Bidtz-Jorgensen E, White RF, et al. Methylmercury exposure biomarkers as indicators of neurotoxicity in children aged 7 years. Am J Epidemiol 1999; 150:301-5. 54. Stewart P, Reihman J, Lonkey E, Darvill T, Pagano J. Prenatal PCB exposure and neonatal behavioral assessment scale (NBAS) performance. Neurotoxicol Teratol 2000; 22:21-9. 55. Tang HW, Huel G, Campagna D, Hellier G, Boissinot C, Blot P. Neurodevelopmental evaluation of 9-month-old infants exposed to low levels of lead in utero: involvement of monoamine neurotransmitters. J Appl Toxicol 1999; 19:167-72. Corresponding author Alicelebic Selma Institute of Histology and Embryology, School of Medicine, University of Sarajevo, Bosnia and Herzegovina E-mail: [email protected]


651