Lead alters intracellular protein signaling and suppresses pro-inflammatory activation in TLR4 and IFNR-stimulated murine RAW 264.7 cells, in vitro.

Lead (Pb) is a persistent environmental pollutant that has a structure and charge similar to many ions, such as calcium, that are essential for normal cellular function. Pb may compete with calcium for protein binding sites and inhibit signaling pathways within the cell affecting many organ systems including the immune system. The aim of the current study was to assess whether the calcium/calmodulin pathway is a principal target of environmentally relevant Pb during pro-inflammatory activation in a RAW 264.7 macrophage cell line. RAW 264.7 cells were cultured with 5 µM Pb(NO3)2, LPS, rIFNγ, or LPS+rIFNγ for 12, 24, or 48 hr. Intracellular protein signaling and multiple functional endpoints were investigated to determine Pb-mediated effects on macrophage function. Western blot analysis revealed that Pb initially modulated nuclear localization of NFκB p65 and cytoplasmic phosphorylation of CaMKIV accompanied by increased phosphorylation of STAT1ß at 24 hr. Macrophage proliferation was significantly decreased at 12 hr in the presence of Pb, while nitric oxide (NO) was significantly reduced at 12 and 24 hr. Cells cultured with Pb for 12, 24, or 48 hr exhibited altered cytokine levels after specific stimuli activation. Our findings are in agreement with previous reports suggesting that macrophage pro-inflammatory responses are significantly modulated by Pb. Further, Pb-induced phosphorylation of CaMKIV (pCaMKIV), observed in the present study, may be a contributing factor in metal-induced autophagy noted in our previous study with this same cell line.

Exposure of juvenile Leghorn chickens to lead acetate enhances antibiotic resistance in enteric bacterial flora.

Heavy metals have been implicated for their ability to increase antibiotic resistance in bacteria collected from polluted waters, independent of antibiotic exposure. Specific-pathogen-free Leghorn chickens were therefore given Pb acetate in the drinking water to expose the enteric bacteria to Pb and to determine if antibiotic resistance changed in these bacteria. Concentrations of Pb used were 0.0, 0.01, 0.1, 1.0, or 10.0 mM; birds given the highest 2 concentrations showed signs of moribundity and dehydration and were removed from the study. Vent culture samples were collected for bacterial cultures on d 0 before Pb exposure, d 7 and 14, and then birds were euthanized by CO2 gas for necropsy on d 14, at which time intestinal contents were also collected for bacterial cultures. Fecal swabs but not intestinal samples from Pb-exposed birds contained isolates that had significantly elevated antibiotic resistance. Some of the isolates contained bacteria that were resistant to up to 20 antibiotics. These results suggest the need for repeated studies in chickens infected with zoonotic pathogens.

Lead at 2.5 and 5.0 µM induced aberrant MH-II surface expression through increased MII exocytosis and increased autophagosome formation in Raw 267.4 cells.

Aberrant major histocompatibility complex class II (MHC-II) surface expression on antigen presenting cells (APCs) is associated with dysregulated immune homeostasis. Lead (Pb) is known to increase MHC-II surface expression on murine peritoneal macrophages ex vivo at concentrations exceeding 25 µM. Little data exist examining this effect at physiologically relevant concentrations. To address this deficit, we examined the effects of Pb on MHC-II surface expression, secondary T-cell activation markers (CD80, CD86, CD40), cell viability, cellular metabolic activity, and ß-hexosaminidase activity in RAW 267.4 macrophage cell lines, with changes in cell ultrastructure evaluated by electron and confocal microscopy. Pb induced an increase in MHC-II, CD86, and lysosome-associated LAMP-1 and LAMP-2 surface mean expression during one doubling cycle (17 h), which was mirrored by increased ß-hexosaminidase activity. Although cell viability was unaffected, cellular metabolism was inhibited. Electron microscopy revealed evidence of lipid vacuolization, macroautophagy and myelin figure formation in cells cultured with either Pb or LPS. Confocal microscopy with antibodies against LC3B showed a punctate pattern consistent with the presence of mature autophagosomes. Collectively, these data suggest that 2.5-5.0 µM Pb increased MHC-II surface expression by inhibiting metabolic activity, inducing autophagy, and increasing MHC-II trafficking in a macrophage cell line.

Persistent increase of blood lead level and suppression of δ-ALAD activity in northern bobwhite quail orally dosed with even a single 2-mm spent lead shot.

Birds that display grit ingestion behavior are potentially at risk of lead (Pb) poisoning from mistaken ingestion of spent Pb shot pellets. The majority of available studies designed to assess such risk have used unspent shot pellets rather than field-obtained spent shot, which is oxidized and otherwise changed by weathering. Available studies also often administered more or heavier shot pellets to a bird than it might be expected to ingest. The current study dosed northern bobwhite quail (Colinus virginianus) weighing 194.6 ± 23.1 g (female birds) and 199.3 ± 12.2 g (male birds) with one to three spent no. 9 Pb shot collected from a skeet range, with particular interest in the toxicity that may occur from ingestion of a single 2-mm, 50 mg shot. An 8 week post-dosing clinical observation period was employed, over which feed consumption, body weight, blood Pb levels, and a battery of blood physiological parameters were made. Weight loss occurred in the birds, including male birds dosed with one Pb pellet. Erythrocyte delta aminolevulinic acid dehydratase (δ-ALAD) levels were decreased for the duration of the study across exposures and to levels associated with injury in wild bird populations. Decreased ALAD was particularly severe in female birds dosed with one Pb pellet and was still 92 % decreased at 8 weeks after dosing. Together, these results suggest that inadvertent ingestion of a single no. 9 Pb shot pellet can adversely affect the health of northern bobwhite quail.

Diverse ability of maternal immune stimulation to reduce birth defects in mice exposed to teratogens: a review.

Stimulating the maternal immune system before or during pregnancy can dramatically improve morphologic outcome in mice that have been exposed to teratogens. For example, maternal immune stimulation in mice reduced craniofacial and palate defects, heart defects, digit and limb defects, tail malformations and neural tube defects caused by diverse teratogens that included chemical agents, hyperthermia, X-rays and diabetes mellitus. Several different procedures of immune stimulation were effective and included footpad injection with Freund's Complete Adjuvant, intraperitoneal (IP) injection with inert particles or attenuated Bacillus Calmette-Guerin, intrauterine injection with allogenic or xenogenic lymphocytes, or intravascular, intrauterine or IP injection with immunomodulatory cytokines. Limited information is available regarding mechanisms by which such immune stimulation reduces fetal dysmorphogenesis; however, cytokines of maternal origin have been suggested as effector molecules that act on the placenta or fetus to improve development. These collective data raise novel questions about the possibility of unrecognized maternal immune system regulatory activity in normal fetal development. This manuscript reviews the literature showing maternal immune protection against morphologic birth defects. Potential operating mechanisms are discussed, and the possibility is considered that a suppressed maternal immune system may negatively impact fetal development.

A single mid-gestation exposure to TCDD yields a postnatal autoimmune signature, differing by sex, in early geriatric C57BL/6 mice.

We recently observed an autoimmune profile in 24-week-old C57BL/6 mice that received a 2.5 or 5.0µg/kg mid-gestation dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (Mustafa et al., 2008). The clinical signs were consistent with a lupus-like syndrome and included: increased autoantibody levels, renal IgG and C3 immune complex deposition with associated inflammation, and increased peripheral Vß(+) T cells. No studies currently exist following the progression of such disease into middle or advanced ages, when human autoimmune diseases may manifest. Therefore in the present study, littermates of mice from the previous 24 week prenatal TCDD study were allowed to age to 48 weeks, considered early geriatric in mice. Similarities and differences in the disease profile based on age and sex were observed. Peripheral autoreactive Vß(+) T cells were increased in both sexes at 48 weeks, in contrast to males only at 24 weeks. Activated T cells from 48-week-old prenatal TCDD females over-produced the pro-inflammatory cytokine IFN-γ while males over-produced IL-10, effects again not seen at 24 weeks. Splenic transitional-2 B cells (CD21(int)CD24(hi)) were increased in males while transitional-1 B cells (CD23(neg) CD1(neg)) were increased in females at 48 weeks. Autoantibodies to cardiolipin and CD138(+) spleen plasma cells were significantly increased in the aged males but not females. Anti-IgG and anti-C3 immune complex renal deposition were also significantly increased in the prenatal TCDD males but not females. These selective changes in the aged male mice may be noteworthy, in that the prevalence of SLE in humans shifts dramatically toward males with aging. The collective findings in aged mice suggest that prenatal TCDD permanently biases the postnatal immune response in C57BL/6 mice toward autoimmunity, and support a significant B cell component to the induced renal autoimmune disease.

Detection of polycyclic aromatic hydrocarbons in the shed skins of corn snakes (Elaphe guttata).

Previous work has shown that organochlorine compounds, including chlordane, lindane and polychlorinated biphenyls, and heavy metals, including lead, mercury and cadmium, are readily detected in the shed skins of snakes dosed with these toxicants. This suggested the shed skins may have broad utility as a non-lethal biomarker tissue for environmental contamination. In the present study, two polycyclic aromatic hydrocarbons (PAHs), benzo[a]pyrene (B[a]P) and 3-methylcholanthrene (3-MC), were similarly studied, as representatives of a third major pollutant category of environmental concern. Both compounds were again readily detected in shed snake skins. These collective results suggest considerable environmental contamination information might be obtained from the evaluation of field-collected shed skins. An advantage of such evaluation is that capture, handling or sacrifice of the live animals is not required.

Viability and function in lymphocytes cultured from the horse, chicken, and mouse: effects of different leukocyte enrichment techniques.

Methods of lymphocyte enrichment tend to vary across species, with the most common techniques employed being density-gradient separation and erythrocyte lysis buffer enrichment. In this study, we assessed lymphocyte viability and proliferation of avian, equine, and murine lymphocytes enriched by a commercial density-gradient technique and under identical, standardized culture conditions. The results of this study clearly show that, under identical enrichment and culture conditions, lymphocyte viability and function can be quite different among the equine, bird, and mouse species. Secondly, the type of enrichment technique employed in the mouse can impact the quality of the immune data generated.

Placental oxidative stress alters expression of murine osteogenic genes and impairs fetal skeletal formation.

Fetal and placental developments rely on an intricate balance of nutrients, growth factors, and signaling pathways at precise times in gestation. Disruptions to this balance may result in disease that manifests in adulthood, a situation termed "developmental origins of health and disease". Diet, exercise, and certain chemical exposures during pregnancy increase oxidative stress (OS), and may alter trajectory of fetal osteogenic regulation in a manner that increases risk of adult bone dysfunction. The present study used gestational methylnitrosourea (MNU), a known inducer of OS, in C57BL/6 mice with or without dietary antioxidant quercetin (Q) supplementation. Several key placental genes that influence placental development and fetal osteogenesis (Hgf, Kitl, IFNalpha4, Ifrd, and IL-1beta) were altered by MNU, and largely normalized by Q. MNU treatment also resulted in small fetuses with disproportionately shortened limbs and distal limb malformations, and caused placental endothelial and trophoblast damage. Q was again protective against these fetal and placental pathologies. An unanticipated finding with Q supplementation was increased interdigital webbing, perhaps due to dose-related effects on apoptosis required for digital sculpting, or pro-oxidant effects of Q that caused a maturational delay. These results suggest that elevated OS may alter normal placental osteogenic signaling and fetal skeletal formation.

An enhanced postnatal autoimmune profile in 24 week-old C57BL/6 mice developmentally exposed to TCDD.

Developmental exposure of mice to the environmental contaminant and AhR agonist, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), causes persistent postnatal suppression of T cell-mediated immune responses. The extent to which prenatal TCDD may induce or exacerbate postnatal autoimmune disease remains unknown. In the present study, time-pregnant high affinity AhR C57BL/6 mice received a single oral administration of 0, 2.5, or 5 microg/kg TCDD on gestation day (gd) 12. Offspring of these mice (n=5/gender/treatment) were evaluated at 24 weeks-of-age and showed considerable immune dysregulation that was often gender-specific. Decreased thymic weight and percentages of CD4(+)CD8(+) thymocytes, and increased CD4(+)CD8(-) thymocytes, were present in the female but not male offspring. Males but not females showed decreased CD4(-)CD8(+) T cells, and increased Vbeta3(+) and Vbeta17a(+) T cells, in the spleen. Males but not females also showed increased percentages of bone marrow CD24(-)B220(+) B cell progenitors. Antibody titers to dsDNA, ssDNA and cardiolipin displayed increasing trends in both male and female mice, reaching significance for anti-dsDNA in both genders and for ssDNA in males at 5 microg/kg TCDD. Immunofluorescent staining of IgG and C3 deposition in kidney glomeruli increased in both genders of prenatal TCDD-exposed mice, suggestive of early stages of autoimmune glomerulonephritis. Collectively, these results show that exposure to TCDD during immune system development causes persistent humoral immune dysregulation as well as altered cell-mediated responses, and induces an adult profile of changes suggestive of increased risk for autoimmune disease.

Perinatal TCDD exposure and the adult onset of autoimmune disease.

Modulation of the developing immune system can occur following perinatal exposure to a number of immunotoxic compounds, including polyhalogenated hydrocarbons like 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD; dioxin), the most toxic of the congeners. Studies in rodents have shown immunologic effects from perinatal TCDD exposure are more severe and persistent than following exposure in the adult, and include what appears to be life-long immunosuppression. Whether prenatal TCDD exposure may predispose an individual to postnatal autoimmune disease remains largely unknown. TCDD crosses the placenta and alters normal prenatal thymocyte maturation, T-cell receptor expression and expression of thymic major histocompatability complex Class II molecules. During the juvenile stage, mice exposed to TCDD prenatally show increased peripheral T-cells possessing "autoreactive" variable-beta receptors. These data suggest that gestational exposure to TCDD may interfere with normal development of central tolerance in the thymus. In possible support of this theory, when autoimmune disease-prone mice were treated with TCDD during gestation, postnatal autoimmunity had an accelerated onset and was exacerbated. This review provides an overview of the currently available information, which appears to support a hypothesis for increased risk of postnatal autoimmune responses as a result of TCDD exposure during the sensitive time of immune system establishment.

Does immune stimulation or antioxidant therapy reduce MNU-induced placental damage via activation of Jak-STAT and NFkappaB signaling pathways?

Maternal oxidative balance and immune health impact both placental and fetal developments. The alkylating agent methylnitrosourea (MNU) increases placental oxidative stress and alters fetal development; the proposed mechanism is placental inflammation, endothelial dysfunction, and cell loss resulting in reduced fetal-maternal circulation and fetal hypoxia. Results of the present study suggest two primary cellular signaling pathways associated with placental and fetal malformations in mice following mid-gestational MNU: Jak-STAT and NFkappaB. Activation of these pathways was associated with increased placental granulocyte-macrophage colony stimulating factor (GM-CSF), interleukin-2 (IL-2), IL-4, leptin, macrophage chemotactic protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-alpha), thrombopoietin (TPO), and vasculoendothelial growth factor (VEGF), and decreased IL-10. Maternal immunostimulation with Freund's complete adjuvant (FCA) or interferon-gamma (IFN-gamma), or antioxidant supplementation with butylated hydroxytoluene (BHT) partially restored placental cytokine levels relative to controls, suggesting that maternal immunity and oxidative stress may both contribute to placental dysregulation and fetal maldevelopment following MNU.

Impact of different cell isolation techniques on lymphocyte viability and function.

The outcome of immunological assays is markedly influenced by the method of isolation of lymphocytes. It is, therefore, important to comparatively assess various techniques of isolation of lymphocytes, an aspect thus far not thoroughly addressed. In particular, the potential of isolation techniques to influence cell recovery, viability, and function has not yet been evaluated. These studies were designed to determine the effect of different mechanical tissue dissociation methods on the viability and function of lymphocytes. Following spleen and thymus removal, the lymphoid organs were dissociated by one of four different tissue dissociation techniques: metallic screen, sheer force slide, commercial stomacher, or plunger-screen. Cells were then enumerated and a trypan blue exclusion technique and 7-amino-actinomycin D (7-AAD) were both employed to assess viability. Mitogen-induced lymphocyte proliferation was measured using the Alamar Blue assay. Cell viability and lymphocyte surface antigen expression were assessed using flow cytometry. No significant differences in lymphocyte viability, morphology, or surface antigen expression were observed among the different techniques. Likewise, cellular apoptosis and necrosis were comparable across all the techniques. However, mitogen induced splenic T-cell proliferation was higher in cells collected using the metallic screen and plunger-screen isolation methods as compared to the sheer force slide or commercial stomacher procedures. These data suggest that cell recovery, morphology, and viability are not affected by isolation techniques. However, lymphocyte function, as assessed by mitogen induced proliferation, was negatively affected by the sheer force slide or commercial stomacher isolation techniques.

Excretion of three heavy metals in the shed skin of exposed corn snakes (Elaphe guttata).

Three heavy metals of regional environmental concern-lead, cadmium, and mercury-are frequently evaluated as part of wildlife bioaccumulation and health monitoring studies. Shed skins of snakes may represent a useful, nonlethal biomarker tissue for such determinations. In the present study, these three heavy metals were injected into thawed mice that were fed to corn snakes (Elaphe guttata) such that snakes received 2mg/kg of each metal/month. Shed skins were collected over a period of 34 weeks, and levels of the heavy metals were determined in skins by atomic absorption methods. Each heavy metal was readily detected in the shed skins, with mean levels as follows: lead 234 ppb, cadmium 806 ppb, and mercury 403 ppb. Control snakes that were fed nonmetal-injected mice produced shed skins that contained mean levels of 6, 12, and 20 ppb lead, cadmium, and mercury, respectively. These detection levels corresponded closely to expected trace metal contents of mouse chow and tap water. These results demonstrate that dietary metal exposure can be readily detected in shed snake skins, including at trace levels of exposure that may be consistent with, or below, environmental exposures.

Role of maternal dietary antioxidant supplementation in murine placental and fetal limb development.

Methylnitrosourea (MNU) is a multisystem teratogen that damages proliferating cells through macromolecule alkylation and generation of reactive oxygen species (ROS). Murine dams exposed to MNU midgestation produce offspring with distal limb malformations, an outcome reduced by maternal immune stimulation. Immunostimulatory effects of antioxidant therapy may in part explain this improved birth outcome. The present study hypothesizes that placental, rather than fetal, damage from excessive ROS may contribute to MNU-induced embryopathy. Fetal limbs and placentas were examined in immunotolerant CD-1 and immunosensitive C57BL/6N mice exposed to MNU, dietary antioxidant butylated hydroxytoluene (BHT), or both. MNU increased fetal resorptions and incidence of syndactyly, oligodactyly, polydactyly, and interdigital webbing, and decreased fetal size in both mouse strains. BHT reduced syndactyly and oligodactyly in both strains, and reduced polydactyly in C57BL/6N mice. Increased webbing in MNU and MNU+BHT groups likely represented maturational delay. Placentas from CD-1 and C57BL/6N MNU-exposed dams demonstrated decreased trophoblasts and increased necrosis of endothelium. Similar to distal limb defects, placental damage was reduced in mice receiving MNU+BHT. These results suggest that placental damage and fetal defects caused by MNU are in part ROS-mediated, and reduced distal limb defects following MNU+BHT may be related to improved placental integrity and function.

Combined dermal exposure to permethrin and cis-urocanic acid suppresses the contact hypersensitivity response in C57BL/6N mice in an additive manner.

Cutaneous exposure to the pyrethroid insecticide permethrin significantly suppresses contact hypersensitivity (CH) response to oxazolone in C57BL/6N mice. Additionally, cis-urocanic acid (cUCA), an endogenous cutaneous chromophore isomerized to its active form following exposure to ultraviolet radiation, modulates cell-mediated cutaneous immune responses. This study describes cutaneous immune alterations following combined topical permethrin and intradermal cUCA exposure. Female C57BL/6N mice were administered 5, 50 or 100 microg cUCA daily for 5 consecutive days. CH was then evaluated by the mouse ear swelling test (MEST) response to oxazolone. Decreased responses of 52.3%, 76.3% and 76.3%, respectively, as compared to controls were observed. Then, mice were co-exposed to 5 microg cUCA daily for 5 days and 1.5, 5, 15, or 25 microL permethrin, on either day 1, 3 or 5 of the cUCA treatment to evaluate combined immunomodulatory effects of the two chemicals, or cUCA daily for 5 days followed by permethrin on day 3, 5, or 7 after the last cUCA injection to demonstrate prolonged immunosuppressive effects. Two days after final treatment, mice were sensitized with oxazolone and MEST was performed. Mice receiving five cUCA injections and permethrin topically on cUCA injection day 1 showed up to 93.3% suppression of MEST compared to vehicle control. CH was suppressed by 87.5%, 86.6% and 74.2% in mice treated with 25 muL permethrin on days 3, 5 and 7 after cUCA, respectively, compared to vehicle control. Taken together, these data indicate co-exposure to cUCA and permethrin profoundly suppresses cell-mediated cutaneous immunity.

Early pesticide exposure and later mortality in rural Africa: a new hypothesis.

Season of birth correlates with approximately 10-fold increased risk of early mortality from infectious disease in parts of The Gambia, West Africa. The increased early death occurred in individuals aged 25-50, who were born during the nonharvest season when stored groundnuts constituted a significant portion of the diet. Insect pests destroy stored groundnuts if not prevented, thus, the people mix insecticides into the storage bags before sealing of the bags. This procedure has been used since the 1970s or earlier, with the specific insecticide agents varying by availability. Organochlorine insecticides including DDT, lindane, and chlordane were added to bags until as recently as the 1980s. Subsequently organophosphates and pyrethroids became available and largely replaced the organochlorine agents. These agents both cross the placenta and are secreted into milk. Further, all are recognized immunotoxicants. These collective observations suggest the possibility that perinatal immunotoxic pesticide exposure, in individuals born during nonharvest months, may impair development of the immune system and increase risk of early death from infectious disease. Additional studies are planned to investigate our hypothesis that pesticide-related developmental immuntoxicity may contribute, in part, to Gambian seasonal mortality.

Tetrachlorodibenzo-p-Dioxin (TCDD) Inhibits Differentiation and Increases Apoptotic Cell Death of Precursor T-Cells in the Fetal Mouse Thymus.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) causes thymic atrophy as well as alterations in thymocyte maturity in mice. Multiple mechanisms for thymic hypocellularity have been suggested, and include an increase in thymocyte apoptosis, a maturation arrest of thymocyte development, inhibited thymocyte proliferation, and a diminution of seeding of the thymus by the hematopoietic progenitors in the fetal liver or adult bone marrow. Fetal mice are highly sensitive to hypocellularity induction by TCDD when the chemical is administered during the window of thymic development, between days 10 and 18 of gestation. Treatment of pregnant C57Bl/6 mice in the present experiments with doses of 5 or 10 mu g/kg TCDD by oral gavage on gestation days 14 and 16 severely depressed day 18 thymic cellularity. Histopathologic evaluation of day 18 fetal thymi showed disruption of the normal organ architecture with loss of clear distinction between cortical and medullary regions after TCDD. A decrease in thymocyte density was noted in all regions, and was most dramatic in the cortical zones where pyknotic cells were increased by TCDD treatment. Using day 18 thymocyte suspensions and flow cytometry, the marker 7-AAD showed a decrease in viable thymocytes from TCDD-treated fetal mice, and a concomitant and dose-related increase of thymocytes in early apoptosis. Specifically, relative to control, thymocytes from the 5 and 10 mug/kg TCDD exposure groups displayed 1.9% and 5.3% respective increases in early apoptotic cells. When thymocytes were co-identified by CD4 and CD8 cell surface antigen expression, the enhanced apoptosis occurred in the CD4(+)CD8(+) phenotype with no significant apoptosis seen in the CD4(-)CD8(-), CD4(+)CD8(-), or CD4(-)CD8(+) thymocytes. Given the rapid clearance of apoptotic cells from the thymus, these histopathologic and cytometric data suggest increased thymocyte apoptosis contributes to fetal thymic atrophy after TCDD exposure.

Organochlorine detection in the shed skins of snakes.

Lizards and snakes eliminate heavy metals in their shed skins. There are no data with regard to reptilian skin as a depuration route for organochlorine (OC) compounds; however, birds deposit OCs in feathers. Corn snakes (Elaphe guttata) were therefore fed thawed mice that had been injected with a mixture of alpha-chlordane, Aroclor 1254 (a polychlorinated biphenyl (PCB) mixture), and lindane (gamma-hexachlorocyclohexane) at 2, 8, and 4 mg/kg, respectively. Feeding of contaminated mice occurred on the first weekly feeding of each month, with remaining weekly feedings consisting of noncontaminated mice, and was continued for 6 months. Shed skins were evaluated in a multiresidue OC scan by gas chromatography. All three chemical contaminants were readily detected in the shed skins: chlordane, 0.155-0.213 ppm; PCB, 3.49-7.01 ppm; lindane: 0.028-0.042 ppm. These data suggest that the shed skin of snakes may serve as an elimination route for OC contaminants and as such may have utility as a noninvasive, nondestructive indicator tissue for assessing environmental contamination.