Environmentally-relevant Levels Research Articles

Effects of Arsenic and Cadmium on the Post Larvae of Giant Freshwater Prawn (Macrobrachium rosenbergii) a Preliminary Study

Arsenic (As) and Cadmium (Cd) are two of the heavy metals that gained public and nationalattention of the Sri Lankan community. Globally, As and Cd are reported as two of the mosttoxic heavy metals that cause physiological and biochemical alterations and mortality inexposed organisms. Cadmium levels in the range of 0.001 to 0.138 mg l-1 have been reportedin both ground and surface water sources of Sri Lanka. Few studies in the country havedocumented levels of arsenic in natural water bodies. Furthermore, studies assessing thepotential toxicity of these two metals to species that are of importance to Sri Lanka, arescarce. The aim of this preliminary study was to investigate the effects of environmentallyrelevant levels of As and Cd on the commercially exploited fresh water prawnMacrobrachium rosenbergii, using its post larvae, which are initially released into reservoirsin Sri Lanka. Post larvae were collected from a culture facility in Pambala, Chilaw and weremaintained in glass beakers. They were acclimatized before use for 96 hr acute toxicity trials,where they were exposed to a series of concentrations of either As (from 0.001 to 0.08 mg l-1)and Cd (from 0.001 to 0.05 mg l-1). Constant experimental conditions were maintained inboth the control and treatment, each conducted in triplicate.The results show that the heavy metals at the tested concentrations induced significantlyhigher levels of mortality (p<0.05). For instance, the lowest test level of As (0.001 mg l-1)induced a twofold higher level of mortality (50%) than the control (20 %), whilst that withthe lowest level of Cd was also similarly high (46.7 %). A strong and positive dose dependenttrend (R2 = 0.87; p<0.05) was, however, evident only for Cd. Comparing the toxicity of theheavy metals in terms of inducing mortality, Cd appears to be potentially more toxic than As.A level of 0.05 mg l-1 of Cd induced 99 % mortality in the post larvae, whilst a higher level ofAs (0.08 mg l-1) induced only around 56 % mortality. It is interesting that both heavy metalsdid not cause marked alterations in growth with no significant differences being evidentbetween the body sizes of the control and treated larvae after exposure. It should however benoted that there was a greater deviation in body sizes in treated larvae than in those of thecontrol, indicating that there may be differential sensitivity among the individual larvae. Theresults of this study are important since heavy metal pollution may threaten the incomegenerating capacity of Sri Lanka’s inland reservoir fishery.

Environmental exposure to arsenic may reduce human semen quality: associations derived from a Chinese cross-sectional study

BackgroundRecent observations in in vitro and in vivo models suggest that arsenic (As) is an endocrine disruptor at environmentally-relevant levels. When exposed to As, male rats and mice show steroidogenic dysfunction that can lead to infertility. However, the possible effects of As on human male semen quality remain obscure.MethodsWe monitored the profile of As species in the urine of a reproductive-age human cohort and assessed its association with semen quality. Men (n = 96) were recruited in an infertility clinic from July 2009 to August 2010 in the Affiliated Hospital of Chongqing Institute for Population and Family Planning. Five urinary As species were analyzed by high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS). Clinical information on the semen volume, sperm concentration and motility was employed to catalogue and evaluate semen quality according to WHO guidelines. As species concentrations in addition to other continuous variables were dichotomized by the medians and modelled as categorical variables in order to explore using the binary logistic regression possible associations between As exposure and semen quality.ResultsUrinary concentrations (geometric mean ± SD, μg g-1 creatinine) of different As species were 7.49 (±24.8) for AsB, 20.9 (±13.7) for DMA, 2.77 (±3.33) for MMA, and 4.03 (±3.67) for Asi (AsiIII and AsiV). DMA concentrations above the median were significantly associated with below-reference sperm concentrations (P =0.02) after adjusting for age, body mass index (BMI), abstinence, smoking and drinking habits. In addition, smoking was positively associated with MMA.ConclusionReduced parameters in human semen quality are positively associated with As exposure in a reproductive-age Chinese cohort.

Selenocompounds in juvenile white sturgeon: Evaluating blood, tissue, and urine selenium concentrations after a single oral dose

Selenium (Se) is an essential micronutrient for all vertebrates, however, at environmental relevant levels, it is a potent toxin. In the San Francisco Bay-Delta, white sturgeon, an ancient Chondrostean fish of high ecological and economic value, is at risk to Se exposure. The present study is the first to examine the uptake, distribution, and excretion of various selenocompounds in white sturgeon. A combined technique of stomach intubation, dorsal aorta cannulation, and urinary catheterization was utilized, in this study, to characterize the short-term effects of Se in the forms of sodium-selenate (Selenate), sodium-selenite (Selenite), selenocystine (SeCys), l-selenomethionine (SeMet), Se-methylseleno-l-cysteine (MSeCys), and selenoyeast (SeYeast). An ecologically relevant dose of Se (∼500μg/kg body weight) was intubated into groups of 5 juvenile white sturgeon. Blood and urine samples were repeatedly collected over the 48h post intubation period and fish were sacrificed for Se tissue concentration and distribution at 48h. The tissue concentration and distribution, blood concentrations, and urinary elimination of Se significantly differ (p≤0.05) among forms. In general, organic selenocompounds maintain higher blood concentrations, with SeMeCys maintaining the highest area under the curve (66.3±8.7 and 9.3±1.0μgh/ml) and maximum Se concentration in blood (2.3±0.2 and 0.4±0.2μg/ml) in both the protein and non-protein bound fractions, respectively. Selenate, however, did not result in significant increase of Se concentration, compared with the control, in the protein-bound blood fraction. Regardless of source, Se is preferentially distributed into metabolically active tissues, with the SeMet treated fish achieving the highest concentration in most tissues. In contrast, Selenite has very similar blood concentrations and tissue distribution profile to SeCys and SeYeast. From blood and tissue Se concentrations, Selenate is not stored in blood, but taken up rapidly by the liver and white muscle. Urinary elimination of Se is form dependent and peaks between 3 and 12h post intubation. A basic understanding of the overall Se absorption, distribution, and elimination is provided through monitoring tissue Se concentrations, however, conclusions regarding to the dynamics and the specific processes of Se metabolism can only be inferred, in the absence of kinetic information.

Thyroid disruption effects of environmental level perfluorooctane sulfonates (PFOS) in Xenopus laevis

Perfluorooctane sulfonate (PFOS), one of the emerging persistent organic pollutants (POPs), has caused growing international concern especially related to the potential disruption in the development and function of thyroid system. Xenopus laevis is an amphibian species widely used as a suitable amphibian model for thyroid disruption research. To study the thyroid disruption effects related to PFOS exposure at environmental low levels, X. laevis tadpoles were exposed to 0.1, 1, 10 and 100 μg/l PFOS in water respectively from stage 46/47 to stage 62. The results showed that the time to metamorphosis (presented by forelimb emergence, FLE) did not significantly change with PFOS exposure, but exhibited an increasing trend (except for 10 μg/l exposure). Partial colloid depletion was observed for PFOS exposure, but no significant histological abnormality was observed in treatment groups. In addition, PFOS exposure resulted in up-regulation of thyroid hormone-regulated genes-thyroid receptor beta A (TRβA), basic transcription element-binding protein (BTEB) and type II deiodinase (DI2) mRNA expression, presented as an inverted U-shaped dose response pattern. However, the mRNA expression of type III deiodinase (DI3) remained unaffected compared with the control. These results demonstrated that PFOS might disrupt the thyroid system in X. laevis tadpoles regarding FLE changes and regulation alternation of thyroid hormone-regulated genes. Our study has raised new concerns for possible thyroid disruption of PFOS in amphibians at environmental relevant levels.

Effects of environmentally-relevant levels of perfluorooctane sulfonate on clinical parameters and immunological functions in B6C3F1 mice

In the first part of a series of studies to account for perfluorooctane sulfonate (PFOS)-induced sheep red blood cell (SRBC)-specific immunoglobulin M (IgM) antibody suppression in mice, a survey of clinical and immunotoxicological endpoints was examined. Adult female B6C3F1 mice were exposed orally for 28 days to a total administered dose (TAD) of 0, 0.1, 0.5, 1, or 5 mg PFOS/kg. Uterus wet weight was significantly decreased compared with control at the 5 mg/kg dose. No indications of wasting syndrome, malnutrition, alteration of thyroid homeostasis, or signs of overt toxicity were observed. Numbers of splenic CD19+/CD21−, CD19+/CD21+, B220+/CD40+, CD4+/CD154−, CD4+/CD154+, and MHC-II+ cells were not altered. Additionally, ex vivo interleukin-4 (IL-4), IL-5, and IL-6 production by in vitro anti-CD3- or phorbol myristate acetate-stimulated CD4+ T-cells was not affected. Ex vivo IL-6 production by B-cells was significantly increased by in vitro stimulation with either anti-CD40 or lipopolysaccharide. Increased IL-6 production by B-cells was the most sensitive endpoint assessed resulting in alterations at the lowest dose tested (0.1 mg/kg TAD) following anti-CD40 stimulation. Further studies are required to characterize effects on inflammatory markers such as IL-6 at environmentally relevant concentrations of PFOS and to determine the key events associated with PFOS-induced IgM suppression to address potential human health risks.

Assessment of the impact of 2,4-dichlorophenoxyacetic acid (2,4-D) on indigenous herbicide-degrading bacteria and microbial community function in an agricultural soil

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) may influence soil microbial communities by altering the balance between resident populations. Our objective was to assess the effect of environmentally relevant levels (ERLs) of 2,4-D on microbial community function and on the population dynamics of 2,4-D degrading bacteria using a microcosm approach. The most probable number approach was used to enumerate 2,4-D-degrading soil bacteria. Carbon substrates utilization was tested with a microtiter-based oxygen sensor system to evaluate short-term functional shifts caused by herbicide treatment. Shifts in the community in response to potential toxicity of 2,4-D were assessed in the agricultural soil and a reference forest soil using the pollution-induced community-tolerance (PICT) approach. Results indicated that the agricultural soil had a stable 2,4-D degrading population able to use the herbicide as C and energy source, which increases immediately after an ERL dose of 2,4-D and remains high for about 1 month after exposure has ceased. An enhanced, dose-dependent response to 2,4-D as substrate was observed in the microtiter assay, while heterotrophic bacterial activity appeared mostly unchanged. The PICT assay showed higher tolerance to 2,4-D in the agricultural soil than in the unexposed forest soil. Our results suggest that agricultural use of 2,4-D at recommended level leads to selection for (1) a copiotrophic degrader population and (2) a persistently herbicide-tolerant, but functionally similar, microbial community.

Polycyclic aromatic hydrocarbons from diesel emissions exert proallergic effects in birch pollen allergic individuals through enhanced mediator release from basophils

Diesel exhaust particles (DEPs) act as adjuvants in the immune system and contribute to the increased prevalence and morbidity of asthma and allergic rhinitis. Polycyclic aromatic hydrocarbons (PAHs) are major components of DEPs, which may be involved in the induction and enhancement of proallergic processes. In this study we explored adjuvant effects of DEP-PAHs on activation parameters of human basophils, fostering allergic inflammation through the release of preformed or granule-derived mediators. Heparinized blood samples from birch pollen allergic and control donors were stimulated with Bet v 1, the major allergen of birch pollen grains, alone or together with a mixture of 16 environmental prominent PAHs (EPA-PAH standard). Flow cytometric analysis was performed for quantitative determination of PAH-enhanced basophil activation. To assess direct PAH effects on basophils, enriched cultures from both donor groups were exposed to benzo[a]pyrene (B[a]P) or phenanthrene (Phe), two major DEP-PAHs, with and without allergen. Supernatants were assayed for IL-4 and IL-8 secretion and histamine release by means of ELISA. At environmental relevant exposure levels EPA-PAH standard synergized with antigen and significantly enhanced basophil activation of all birch pollen allergic individuals up to 95%. Single PAHs significantly drove IL-8 secretion from sensitized basophils of all patients tested, and there was no further enhancement by addition of rBet v 1. B[a]P and Phe also significantly induced IL-4 secretion, a key factor for Th2 development, from purified sensitized basophils in the absence of antigen suggesting an adjuvant role of DEP-PAHs in allergic sensitization. None of the basophil samples from healthy controls showed any PAH effect on mediator release. DEP-PAHs exert proallergic effects on sensitized basophils in an allergen independent fashion, suggesting a potential role of these pollutants for the allergic breakthrough in atopic individuals, who have not developed an allergic disease yet.

Dinitrobenzene Isomers Structure‐ Dependent Stimulation of Neuronal Nitric Oxide Synthase Catalyzed Electron Flux in the Absence of Calmodulin

Neuronal nitric oxide synthase (nNOS) requires calmodulin (CaM) ‐ binding for efficient electron transfer converting L‐arginine to L‐citrulline and nitric oxide. The present studies focus on electron transfer to and through CaM‐free nNOS. Turnover rates (min−1) of nNOS‐mediated NADPH oxidation (NADPHox) and acetylated cytochrome‐c reduction (AcCyt‐cred) were used to estimate total electron flux and O2. production. Dinitrobenzenes (DNBs) stimulated the rate of NADPHox by CaM‐free nNOS in an isomer‐ and concentration‐ dependent manner. Rates for NADPHox by CaM‐free nNOS at the limit of solubility of the DNBs (160 ?M) were 189 ± 5 min−1, 94 ± 3 min−1 and 38 ± 2 min−1 for 1,4‐, 1,2‐ and 1,3‐DNB, respectively, compared to the solvent control (7 ± 1 min−1). Highly stimulated rates of AcCyt‐cred were observed in presence of all the three DNBs. The nNOS reductase construct without the CaM binding domain (aa 745‐1729) behaved in a manner similar to holo‐nNOS in the presence of DNBs, in the NADPHox and AcCyt‐cred assays. These results indicate that CaM‐free nNOS generates ROS at environmentally‐relevant levels of DNBs (ASTDR). Considering the absolute amount of constitutive NOS expressed in organisms; chronic exposure to low levels of DNBs may lead to continuous oxidative stress.Supported by ES011982 and RR008124 to RTM and UTEP respectively.

Antagonism of TCDD-induced ethoxyresorufin- O-deethylation activity by polybrominated diphenyl ethers (PBDEs) in primary cynomolgus monkey ( Macaca fascicularis) hepatocytes

Polybrominated diphenyl ethers (PBDEs) are widespread environmental pollutants, and the levels of certain congeners have been increasing in biota and abiota in recent decades. Some PBDEs are lipophilic and persistent, resulting in bioaccumulation in the environment. Their structural similarity to other polyhalogenated aromatic hydrocarbons (PHAHs) such as polychlorinated biphenyls (PCBs) has raised concerns that PBDEs might act as agonists for the aryl hydrocarbon receptor (AhR). Recent studies in our laboratory with human and rat cell lines indicated no AhR mediated CYP1A1 induction for PBDEs. However, an earlier in vitro study by Van der Burght et al. (1999) [Van der Burght, A.S., Clijsters, P.J., Horbach, G.J., Andersson, P.L., Tysklind, M., van den Berg, M., 1999. Structure-dependent induction of CYP1A by polychlorinated biphenyls in hepatocytes of cynomolgus monkeys ( Macaca fascicularis). Toxicol. Appl. Pharmacol. 155, 13–23] indicated that in cynomolgus monkey ( M. fascicularis) hepatocytes PCBs with a non-planar configuration could induce CYP1A. As PBDEs show a structural similarity with non-planar ( ortho substituted) PCBs, our present study focused on the possible CYP1A induction by PBDEs (BDE-47, -99, -100, -153, -154, -183, and -77) in individual preparations ( n = 4) of primary hepatocytes of cynomolgus monkeys ( M. fascicularis). 7-Ethoxyresorufin- O-deethylase (EROD) was used as a marker for CYP1A-mediated catalytic activity. Cells were exposed for 48 h to various PBDE concentrations (0.01–10 μM), positive controls 2,3,7,8-TCDD (0.001–2.5 nM) and PCB-126 (0.01–10 nM), and negative control (DMSO vehicle alone). No statistically significant induction of CYP1A was observed in the hepatocytes after 48 h of exposure to all environmentally relevant PBDEs. After exposing hepatocytes to PBDEs in combination with TCDD, a concentration-dependent decrease in TCDD-induced EROD activity was observed. All PBDEs tested showed a similar reduction in each of four experiments, though quantitative differences were observed. The observed antagonism of TCDD-induced EROD activity by PBDEs occurred in both male ( n = 3) and female ( n = 1) hepatocytes and was not due to catalytic inhibition of EROD activity or cytotoxicity. However, based on the results of this study we do not expect these antagonistic effects of PBDEs on CYP1A induction at environmental relevant levels, since these in vitro interactive effects with TCDD were observed only at relatively high concentrations that are normally not seen, e.g. in the human body.

Modulation of endocrine pathways by 4,4′-DDE in the deer mouse Peromyscus maniculatus

4,4′-DDT and 4,4′-DDE are widespread environmental contaminants that cause eggshell thinning in birds, altered sex ratios in the American alligator, and changes in the anal–genital distance in rodents. These contaminants are known to cause some of their toxicity by altering steroid receptor-mediated mechanisms. However, chemical-specific alterations in the expression of hormone-metabolizing enzymes may also be a mechanism for endocrine disruption, by altering the half-life of hormones in critical tissues. Previously, we showed that 4,4′-DDE causes a dose-dependent increase in ethoxyresorufin- O-deethylase (EROD) activity, but not pentoxyresorufin- O-dealkylase (PROD) activity, in the deer mouse. In this study, we demonstrated that 4,4′-DDE elicited a corresponding increase in CYP1A protein expression but not CYP2B using Western blotting and immunoprecipitation. 4,4′-DDE-mediated changes in phase II conjugating enzymes; UDP-glucuronosyltransferase (UGT) and phenolsulfotransferase (ST), were also investigated for the first time. Prepubescent female deer mice were dosed with 4,4′-DDE by gavage on days 1 and 2, then euthanized on day 4. As anticipated, dose-dependent increases in hepatic EROD and MROD activities, but not PROD or BROD, were observed. UGT activity was monitored by incubating liver microsomes and 14C-UDP-GA with potential substrates and measuring incorporation of radioactivity into TLC-resolved glucuronides. Dose-dependent increases in conjugation were observed with p-nitrophenol (a general UGT substrate) but not testosterone. Interestingly, a biphasic dose–response curve was observed for ST activity, with a peak at the 3 mg/kg dose. Dose-dependent increases in CYP1A1 and UGT-specific immunoreactive proteins were observed, suggesting de novo synthesis as a consequence of 4,4′-DDE exposure. We also measured Phase I and II enzymes in deer mouse platelets. Preliminary results indicate that the 4,4′-DDE-induced changes in liver Phase I and II enzyme activity were similar, but not identical, to those found in platelets. These results indicate that environmentally-relevant levels of 4,4′-DDE modulate the activity and expression of CYP1A1 and phase II enzymes in the deer mouse and that certain changes may be measured non-lethally.