Effects Of Environmental Contaminants Research Articles

Toxicity assessment of 2,4-D and MCPA herbicides in primary culture of fish hepatic cells

In this study, we used primary cultures of fish hepatic cells as a tool for evaluating the effects of environmental contamination. Primary hepatic cell cultures derived from the subtropical fish Metynnis roosevelti were exposed to different concentrations (0.275, 2.75 and 27.5 μg L−1) of the herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA). Cellular respiratory activity was evaluated by polarography using three substrates: 0.5 M glucose, 0.5 M succinate and 0.5 M α-ketoglutarate. Significant changes were observed in cellular oxygen consumption with 0.5 M α-ketoglutarate. Even at low concentrations, 2,4-D and MCPA were potent uncouplers of oxidative phosphorylation. Primary cultures of M. roosevelti liver cells may provide a useful tool for the evaluation of environmental contaminant effects. A review of regulations regarding permitted concentrations of these herbicides is needed.

Neotropical electric fishes (Gymnotiformes) as model organisms for bioassays

Electric fishes (Gymnotiformes) inhabit Central and South America and form a relatively large group with more than 200 species. Besides a taxonomic challenge due to their still unresolved systematic, wide distribution and the variety of habitats they occupy, these fishes have been intensively studied due to their peculiar use of bioelectricity for electrolocation and communication. Conventional analysis of cells, tissues and organs have been complemented with the studies on the electric organ discharges of these fishes. This review compiles the results of 13 bioassays developed during the last 50 years, which used the quickness, low costs and functionality of the bioelectric data collection of Gymnotiformes to evaluate the effects of environmental contaminants and neuroactive drugs. journal homepage: www.jclmm.com

Effect of environmental contaminants on mammalian testis.

Exposure of humans and wildlife to pollutants released in the environment is a centre of attention nowadays. Many of these chemicals (generally referred to as environmental pollutants) have been shown to interfere with normal hormonal signalling and biological functions, leading to reproductive disorders or infertility, which has been a matter of concern within the recent decades. The present paper reviews adverse effects of these toxicants on mammalian testes, with emphasis on alteration of steroidogenesis, spermatogenesis, and histopathological effects. From the publications reviewed, it appears that environmental toxicants, especially heavy metals and organic chemicals of synthetic and microbiological origins, disrupt hormone production and action in the mammalian testes. Endocrine disruption leads to disorders of testicular function and thereby compromises the normal phenotypic development of male sexual characteristics, initiation and maintenance of spermatogenesis. The toxicants also induce impairment of testicular cells function, testicular histology, and sperm cells function directly. The release of the toxicants in the environment is still ongoing, despite alarming quantities that already exist in the atmosphere. If appropriate measures are not taken, their impact on the male reproductive function and especially on testicular function will be more serious.

Physiological condition of juvenile wading birds in relation to multiple landscape stressors in the Florida Everglades: effects of hydrology, prey availability, and mercury bioaccumulation.

The physiological condition of juvenile birds can be influenced by multiple ecological stressors, and few studies have concurrently considered the effects of environmental contaminants in combination with ecological attributes that can influence foraging conditions and prey availability. Using three temporally distinct indices of physiological condition, we compared the physiological response of nestling great egrets (Ardea alba) and white ibises (Eudocimus albus) to changing prey availability, hydrology (water depth, recession rate), and mercury exposure in the Florida Everglades. We found that the physiological response of chicks varied between species and among environmental variables. Chick body condition (short-term index) and fecal corticosterone levels (medium-term) were influenced by wetland water depth, prey availability, region, and age, but not by mercury contamination. However, mercury exposure did influence heat shock protein 70 (HSP70) in egret chicks, indicating a longer-term physiological response to contamination. Our results indicate that the physiological condition of egret and ibis chicks were influenced by several environmental stressors, and the time frame of the effect may depend on the specialized foraging behavior of the adults provisioning the chicks.

Assessment of concentrations and effects of organohalogen contaminants in a terrestrial passerine, the European starling

European starlings (Sturnus vulgaris) are a valuable model species for the assessment of concentrations and effects of environmental contaminants in terrestrial birds. Polybrominated diphenyl ethers (PBDEs) are found in birds throughout the world, but relatively little is known of their concentrations or effects in free-living terrestrial passerines. We used a nest box population of European starlings to 1) measure the variation in egg concentrations of persistent organohalogen contaminants at an agricultural site, and 2) assess whether individual variation in PBDE concentrations in eggs was related to reproductive parameters, as well as maternal or nestling characteristics including body condition, thyroid hormones, oxidative stress, and hematocrit. As PBDEs were the main contaminant class of interest, we only assessed a subset of eggs for other organohalogen contaminants to establish background concentrations. Exposure to organohalogen contaminants was extremely variable over this relatively small study area. Geometric mean wet weight concentrations (range in brackets) of the major contaminants were 36.5 (12–174) ng/g ΣDDT (n=6 eggs) and 10.9 (2–307) ng/g ΣPBDEs (n=14). ΣPCBs at 3.58 (1.5–6.4) ng/g (n=6) were lower and less variable. There were low levels of other organochlorine (OC) pesticides such as dieldrin (2.02ng/g), chlordanes (1.11ng/g) and chlorobenzenes (0.23ng/g). The only form of DDT detected was p,p′-DDE. The congener profiles of PBDEs and PCBs reflect those of industrial mixtures (i.e. DE-71, Aroclors 1254, 1260 and 1262). For all of the contaminant classes, concentrations detected in eggs at our study site were below levels previously reported to cause effects. Due to small sample sizes, we did not assess the relationship between ΣPCBs or ΣOCs and adult or chick condition. We observed no correlative relationships between individual variation in PBDE concentrations in starling eggs and reproductive success, maternal condition, or nestling condition in the corresponding nests.

Boosted regression trees – a way to study mixture effects of environmental contaminants measured in the circulation.

Boosted regression trees – a way to study mixture effects of environmental contaminants measured in the circulation.

Comparative study on trace metal accumulation in the liver of two fish species (Torpedinidae): Concentration–size relationship

Metal concentrations (Hg, Cd, Pb, As, Cr, Cu, Zn and Ni) were measured in the liver of two fish, Torpedo nobiliana (electric ray) and Torpedo marmorata (marbled electric ray), from the Mediterranean Sea in order to comparatively investigate their current pollution status. Maximum mean levels of Hg were detected in electric ray (mean: 2.16μgg−1 ww), while marbled electric ray accumulated especially Cd (mean: 0.06μgg−1 ww), Cu (mean: 3.83μgg−1 ww) and As (mean: 32.64μgg−1 ww). The metal concentrations are similar to those reported in literature, except for Cd, As and Ni. Hg concentrations increased with increasing fish body length in both species, whilst no significant concentration–size relationship was found for other metals. To the best of our knowledge this is the first report providing information on trace metal levels and relationship between concentration and size of these cartilaginous fishes. Future studies on the concentrations and effects of environmental contaminants in various torpedinid species are surely needed.

Associations Between Female Reproductive Traits and Polychlorinated Biphenyl Sediment Concentrations in Wild Populations of Brown Bullhead (Ameiurus nebulosus)

Aquatic contaminants, specifically polychlorinated biphenyls (PCBs), a class of persistent organic contaminants, have been associated with sublethal effects on reproduction in fishes. Female brown bullhead (Ameiurus nebulosus) were used to assess variation in reproductive traits across eight populations differing in sediment sum PCB concentrations in the Lower Great Lakes region. Differences in maternal carotenoid allocation patterns among these populations were also examined. No significant associations were found between sediment sum PCB concentrations corrected for organic content (OC) and reproductive traits. However, egg diameter was negatively correlated with sediment PCB concentrations not corrected for OC, suggesting that observed relationships between sediment sum PCB concentrations and reproductive traits are driven by classes of environmental contaminants whose bioavailability are not predicted by OC, such as metals. An unexpected positive relationship was also found between egg carotenoid concentrations and sediment PCB concentrations. This positive relationship was explained by the maternal allocation of carotenoids based on a negative correlation between female muscle and egg carotenoid concentrations, where females from less contaminated locations had lower egg and greater muscle carotenoid concentrations than those from more contaminated locations. The results of this study identify sublethal effects of environmental contaminants on reproductive life-history traits in female brown bullhead, and investigations of adaptive mechanisms underlying this variation are warranted.

Protein extraction and two‐dimensional gel electrophoresis of proteins in the marine mussel Mytilus galloprovincialis: an important tool for protein expression studies, food quality and safety assessment

Shellfish farming is an important economic activity that provides society with a valuable source of food. Analyses of the protein content and metabolism of shellfish are therefore of utmost importance to monitor the presence and effects of environmental contaminants in these organisms and also to assess food quality and authenticity. The aim of the present study was to compare different protein extraction protocols commonly used in two-dimensional gel electrophoresis (2DE) research and select the most suitable for the analysis of gill and digestive gland proteomes from the marine mussel Mytilus galloprovincialis. High-resolution protein separation was achieved by direct solubilisation of proteins from M. galloprovincialis tissues with urea (7 mol L(-1)), thiourea (2 mol L(-1)), CHAPS (40 g L(-1)), DTT (65 mmol L(-1)) and ampholytes (pH 4-7, 8 mL L(-1)). Subsequent protein identification from 2DE gels by MALDI-TOF/TOF mass spectrometry revealed a high number of proteins with functions in cytoskeleton structure, dynamics and maintenance. Other proteins identified in the 2DE gels are involved in energy production and carbohydrate metabolism, metal transport, chaperones and stress response, cell signalling and regulation, proteolysis and protein transduction. Important protein markers for contaminant and quality assessment of shellfish food products can be analysed using 2DE.

The hidden costs of environmental contamination

Cost is an inevitable, but often overlooked and uncounted, consequence of environmental contamination. Any degradation of the environment, whether it is contamination of air or water, pollution of landfills by toxic waste or exposure of children to hazardous chemicals, carries costs. Among these costs are: 1) direct medical expenses for persons made ill by toxic exposures; 2) indirect health-related costs such as time lost from school or work, costs of rehabilitation and costs of special education; 3) diminished economic productivity in persons whose brains, lungs or other organ systems are permanently damaged by toxic exposures; 4) loss of irreplaceable environmental treasures such as the Everglades or the Black Forest; and 5) the costs of environmental clean-up. A methodology for estimating the costs of diseases caused by environmental contamination was developed in the US in the early 1980s by an expert committee convened by the Institute of Medicine and chaired by Stanford University's Nobel Laureate in Economics, Prof. K. Arrow [1]. The core of this methodology is the calculation of the “fractional contribution” of the environment to causation of a particular disease in a particular population. This environmentally attributable fraction (EAF) is defined as: “the percentage of a particular disease category that would be eliminated if environmental risk factors were reduced to their lowest feasible levels” [2]. The EAF for a particular disease, such as childhood asthma, may be converted to an estimate of the cost of that disease in a particular population using the following equation:![Formula][1] Costs are traditionally divided into direct and indirect health-related costs, and both are included in the calculation. The EAF model has now been used in a series of important cases to assess the costs of environmental and occupational disease. Findings from these analyses have had powerful impacts on the health … [1]: /embed/graphic-1.gif

Environmental contaminants and food safety

Food safety is threatened by numerous contaminants, which can originate from environmental pollution, such as toxic metals and organic halogenated compounds; chemicals used in the production of food, such as pesticides and veterinary drugs; contaminants formed during food production and cooking; contaminants arising from food packaging, or natural toxins in food. Consumers’ perceptions of food-related risks have recently been investigated in the 2010 Eurobarometer. The highest concern was reported for pesticides in fruit, vegetables and cereals, with 72% of the respondents being very or fairly worried. Somewhat fewer people were worried about residues like antibiotics and hormones in meat (70%), pollutants like mercury and dioxins (69%), food poisoning from bacteria (62%) or putting on weight (47%). Adverse effects of environmental contaminants may be displayed as developmental toxicity and endocrine disruption, with fetuses and children being vulnerable target groups. One contaminant, which has attracted much attention, is bisphenol A (BPA) and there is a scientific controversy about the low-dose health risks of BPA. BPA is used in the production of polycarbonate plastics and epoxy resins. Human exposure is mainly from packaged food and beverages. BPA binds to estrogen receptors and also acts through other mechanisms on endocrine function. We have investigated effects of BPA on steroidogenic pathways in the human adrenocortical cell line H295R. Secretion of steroidogenic hormones and intermediates were affected at non-toxic levels of BPA. The effects were mediated by inhibition of CYP17 and CYP21 and expressions of steroidogenic genes were downregulated. This may be an additional mechanism behind the endocrine disruptive effects of BPA. One of the greatest challenges in toxicology today is in predicting the risks associated with chemical mixtures. The exposure to contaminants via the diet occurs as a mixture rather than as individual compounds. Thus, food safety is to a high extent dependant on possibilities to predict risks from mixtures. The two models most frequently used are concentration addition and independent action. The main difference between the two models is the assumption of mode of action of the chemicals in the mixture. In concentration addition it is assumed that the chemicals work through a common mode of action and can be regarded as dilutions of each other. In independent action it is assumed that the chemicals act independently via different mode of actions and the mixture effect is predicted by the probabilities of response of the individual chemicals. We have investigated mixture effects of food-related chemicals on secretion of steroids in the human adrenocortical cell line. The results have been compared to the predicted effects from the two prediction models. In general the chemicals acted in an additive manner on secretion of hormones, which could be predicted by both models.

Effects of Environmental Contaminants and Natural Substances on Vitellogenesis in Tilapia Primary Hepatocytes

The efficacy of estrogenic chemicals and plant materials were assessed to stimulate the vitellogenin (VTG) synthesis in an in vitro system based on primary cultures of hepatocytes from female and E2-primed male Mozambique tilapia, Oreochromis mossambicus. Isolated hepatoyctes treated with nonylphenol (NP), bisphenol-A (BP), octylphenol (OP), hexachlorocyclohexane (HCH) and the combination (ALL) as endocrine-disrupting chemicals (EDCs), Solgen 40®, SG40, as a commercial phytoestrogens and plant extracts (fenugreek, FG; aniseed, AS; safflower, SF; flaxseed, FS; fennel, FN; liqurice, LR; pomegranate, PG; soybean, SB) as natural substances, respectively, and their estrogenic activity were compared to control (ethanol treated hepatoyctes). Hepatic VTG levels in medium were determined by ELISA in the primary hepatocytes culture. All tested compounds induced secretion of VTG in hepatocytes of female as well as male tilapia. The induction of the hepatic response was not statistically different when each compounds was compared to control with HCH from EDCs and FG, AS, FN, LQ and PG from plant extracts in female and all cases of EDCs and plant extracts (except SG40 and SB) in male hepatoyctes. The EDCs and plant materials tested were considerably less potent than estradiol. Sensitive tilapia hepatoycte assay for measuring VTG are valuable tools for identifying the presence of environmental estrogens.

Developmental thyroid hormone disruption: Prevalence, environmental contaminants and neurodevelopmental consequences

Thyroid hormones (TH) are critical for growth and development and particularly brain development. There are numerous environmental agents that lead to marginal reductions of circulating TH. Although it is clear that severe developmental hypothyroidism is profoundly detrimental to neurodevelopment, there is less information regarding the consequences of modest degrees of thyroid. The impact of low level TH disruptions induced by environmental contaminants has not been defined. This paper is a synopsis from four invited speakers who presented at the 13th International Neurotoxicology Association meeting held in Xi’an, China during the summer of 2011. An overview of the role of TH in brain development and a review of human and animal data on the neurological sequelae of disruption of the thyroid axis in the pre- and early post-natal periods were presented by Mary Gilbert and Joanne Rovet. Iodine deficiency, a common cause of TH insufficiency and mental retardation in many countries, including China, was addressed by Zupei Chen. In this presentation the current incidence of iodine deficiency and neurological outcome in China and the efficacy of recently implemented iodinization programs to eliminate this cause of mental retardation were reviewed. Joanne Rovet described the impact of TH disruption during pregnancy and under conditions of congenital hypothyroidism. Children born with normal thyroid function, but who experienced TH insufficiency in the womb, display subtle cognitive impairments and abnormalities in brain imaging. Despite early detection and treatment, deficiencies also exist in children born with thyroid disorders. Different patterns of cognitive effects result from prenatal versus postnatal TH insufficiency. Mary Gilbert reported on the effects of environmental contaminants with thyroid disrupting action on brain development in animals. Results of neurophysiological, behavioral, structural and molecular alterations that accompany modest perturbations of the thyroid axis were reviewed. Noriyuki Koibuchi described molecular targets of TH-mediated signalling accompanying exposure to persistent organic pollutants. Both polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are prevalent environmental contaminants that disrupt TH signalling at the receptor level. This action by these chemical classes could contribute to the negative impact of these chemicals on brain function. In summary, epidemiological, preclinical and animal research has clearly identified the critical role of TH in brain development. Additional work is required to understand the impact of low level perturbations of the thyroid axis to evaluate the risk associated with environmental contaminants with thyroid action.

The effect of environmental contaminants on testicular function

Male reproductive health has deteriorated considerably in the last few decades. Nutritional, socioeconomic, lifestyle and environmental factors (among others) have been attributed to compromising male reproductive health. In recent years, a large volume of evidence has accumulated that suggests that the trend of decreasing male fertility (in terms of sperm count, quality and other changes in male reproductive health) might be due to exposure to environmental toxicants. These environmental contaminants can mimic natural oestrogens and target testicular spermatogenesis, steroidogenesis, and the function of both Sertoli and Leydig cells. Most environmental toxicants have been shown to induce reactive oxygen species, thereby causing a state of oxidative stress in various compartments of the testes. However, the molecular mechanism(s) of action of the environmental toxicants on the testis have yet to be elucidated. This review discusses the effects of some of the more commonly used environmental contaminants on testicular function through the induction of oxidative stress and apoptosis.

Effect of Environmental Contaminants on Beta Cell Function

There is an increasing concern that chemicals in the environment are contributing to the global rise in the prevalence of type 2 diabetes (T2D). However, there is limited evidence for direct effects of these chemicals on beta cell function. Therefore, the goals of this study were (1) to test the hypothesis that environmental contaminants can directly affect beta cell function and (2) examine mechanistic pathways by which these contaminants could affect beta cell function. Using mouse beta TC-6 cells, we examined the acute effects of 6 substances (benzo[a]pyrene, bisphenol A [BPA], propylparaben, methylparaben, perfluorooctanoic acid, and perfluorooctyl sulfone) on insulin secretion. Only BPA treatment directly affected insulin secretion. Furthermore, chronic exposure to BPA altered the expression of key proteins in the cellular and endoplasmic reticulum stress response. These data suggest that long-term BPA exposure may be detrimental to beta cell function and ultimately be an important contributor to the etiology of T2D.

Addressing Environmental Contaminants in Pediatric Practice

1. Catherine Karr, MD, MS, PhD* 1. *Assistant Professor of Pediatrics; Director, Pediatric Environmental Health Specialty Unit, University of Washington, Seattle, WA. After completing this article, readers should be able to: 1. Recognize the basis for children's susceptibility to environmental contaminants. 2. Identify common pediatric environmental health problems. 3. Take an environmental history to discern risks. 4. Access reliable and useful resources on pediatric environmental health topics. 5. Discuss environmental exposure reduction and prevention with patients and families. The past decade has been marked by a rapid expansion of scientific inquiry, media reports, and public interest in the topic of environmental contaminants and child health. There are few pediatric environmental health specialists, and most health conditions associated with contaminants in food, water, the home environment, and the community present initially to the primary care clinician. Consequently, pediatricians are increasingly called on to answer questions about environmental health. Although standard medical education on these topics is limited and self-reported confidence among pediatric clinicians is low, extensive knowledge of toxicology is not required to suspect environmental health problems. This article reviews core concepts of pediatric environmental health, commonly encountered pediatric environmental hazards, and the environmental history. Understanding these areas of knowledge should allow the clinician to develop a degree of suspicion that is the foundation for discerning and preventing the potential adverse effects of environmental contaminants in child health. Children's susceptibility to environmental contaminants differs from that of adults. Pediatricians are familiar with the differences inherent in children across the life stages. Therapeutic interventions such as dosing based on weight or surface area is part of everyday practice. Injury prevention advice for a newborn is unique from that given during an adolescent visit. Similar concepts apply to the potential vulnerability of children to adverse consequences of exposure to environmental contaminants, reinforcing …

Iodine and pregnancy.

Iodine is a necessary element for the production of thyroid hormone. We will review the impact of dietary iodine status on thyroid function in pregnancy. We will discuss iodine metabolism, homeostasis, and nutritional recommendations for pregnancy. We will also discuss the possible effects of environmental contaminants on iodine utilization in pregnant women.

Environmental contaminant effects on juvenile striped bass in the San Francisco Estuary, California, USA

The decline of pelagic organisms in the San Francisco Estuary (SFE) (California, USA) is attributed to several factors, including water diversions, invasive species, and exposure to environmental toxicants. The present study evaluated the effects of environmental contaminants on liver vitellogenin, metallothionein, 7-ethoxyresorufin-O-deethylase (EROD), and benzyloxyresorufin O-deethylase (BROD) activity in juvenile striped bass (Morone saxitilis) in the SFE. Analysis of juvenile striped bass liver extracts revealed site-specific elevations of vitellogenin, metallothionein, and EROD biomarkers across the estuary. Although some striped bass in the estuary showed EROD activity similar to unhandled hatchery controls, several sites in the estuary showed significantly higher EROD activity that was in the range of beta-naphthoflavone (BNF)-injected, positive controls. Overall, EROD activity averaged 283% higher in estuary fish than in hatchery controls. Chemical analyses of extracts from semipermeable membrane devices (SPMDs) deployed in the estuary for one month showed elevated polyaromatic hydrocarbon (PAH) levels. Semipermeable membrane devices extract injections-induced metallothionein and BROD in striped bass livers. These data show that environmental exposures are impacting EROD and other biomarkers in the SFE striped bass population. Previous studies in our laboratory have associated poor larval development with maternal transfer of environmental contaminants. Further studies are needed to monitor contaminant exposures by the use of biomarkers and to integrate them into a more effective pelagic species recovery plan in the SFE.

New aspects on atrazine biodegradation

The world practice of using agrochemicals for long periods, in an indiscriminated and abusive way, has been a concern of the authorities involved in public health and sustainability of the natural resources, as a consequence of environmental contamination. Agrochemicals refer to a broad range of insecticides, fungicides and herbicides, and among them stands out atrazine, a herbicide intensively used in sugarcane, corn and sorghum cultures, among others. Researches have demonstrated that atrazine has toxic effects in algae, aquatic plants, aquatic insects, fishes and mammals. Due to the toxicity and persistence of atrazine in the environment, the search of microbial strains capable of degrading it is fundamental to the development of bioremediation processes, as corrective tools to solve the current problems of the irrational use of agrochemicals. This review relates the main microbial aspects and research on atrazine degradation by isolated microbial species and microbial consortia, as well as approaches on the development of techniques for microbial removal of atrazine in natural environments.

Oxyradical scavenging capacity by the S9 fraction of Hexagenia spp. nymphs from the Western Basin of Lake Erie: neutralisation of three potent oxidants

Oxidative stress is a general response of aquatic organisms to environmental contamination. Metals and organic compounds capable of redox cycling cause proliferation of reactive oxygen species (ROS) within organisms. Harm results from ROS-mediated DNA damage, lipid peroxidation, enzyme degradation and compromised intermediary metabolism. Variations in concentrations or activities of antioxidants have been proposed as biomarkers of toxicant-mediated oxidative stress in aquatic organisms. The total oxyradical scavenging capacity (TOSC) assay provides an index of biological resistance to ROS. Burrowing mayflies (Hexagenia spp.) are key indicator species of the health of numerous water bodies, including Lake Erie. TOSC has been used to evaluate the ROS scavenging capacity of tissues from a number of marine and freshwater invertebrates. This is the first study to evaluate ROS scavenging capacity in Hexagenia nymphs. Hexagenia nymphal tissue was homogenised in TRIS buffer containing a protease inhibitor cocktail and then differentially centrifuged to obtain a 9000 g supernatant (S9). The specific TOSC values (±SD, n=3) per μg protein are 2.08±0.43 for peroxyl radicals, 3.06±0.19 for hydroxyl radicals and 0.36±0.02 for peroxynitrite (n=3 to 4 determinations). These values for peroxyl radical scavenging capacity were equivalent to 11.9% and 77.0% that of Trolox (a water soluble analogue of vitamin E) and reduced glutathione TOSC equivalents, respectively, on a per μg basis. These results show that Hexagenia nymphal S9 is capable of neutralising peroxyl radicals and hydroxyl radicals effectively, but neutralises peroxynitrite considerably more weakly. The efficacy of this parameter as a biomarker of exposure to or effect of environmental contaminants will require controlled exposure analysis.