Observable Adverse Effect Concentration Research Articles

Differences in the effects of sodium selenate and sodium selenite on the mortality, reproduction, lipid peroxidation and glutathione redox status of Folsomia candida Willem 1902 (Collembola)

The average selenium content of the soils worldwide is 0.4 mg kg−1; however, the selenium concentration can be much higher in some areas. Selenium is essential to humans and animals, but it can also be a risk based on the narrow gap between the beneficial and toxic concentrations. There is scarce information in the literature on the effects of various inorganic forms of selenium on soil invertebrates, such as collembolans. Consequently, the goal of our study was to determine if selenium has a negative effect on the collembolan species Folsomia candida and to verify if there is a difference between the effects of the two oxidation forms. The effect of sodium selenite and sodium selenate on Folsomia candida was studied in the laboratory by mortality and reproduction tests also by various sub-lethal and biochemical methods. The methods used in our study included a standard OECD test according to the 232 guideline, and we measured the life history parameters such as relative growth, egg production, and egg volume. For the investigation of lipid peroxidation and glutathione redox status, malondialdehyde (MDA) content, reduced glutathione (GSH) concentration and glutathione peroxidase (GPx) activity were measured. Our results showed that up to a concentration of 0.5 mg kg−1 Se in soil, both selenium forms were beneficial for F. candida. For mortality, the LOAEC (lowest observable adverse effect concentration) was 8 mg kg−1 Se in the soil in the experiments according to the OECD 232 test for both selenium forms. In case of juveniles, sodium selenite was much more toxic than sodium selenate. The LOAEC was 0.5 mg kg−1 for sodium selenite and 8 mg kg−1 in the case of sodium selenate. Sub-lethal parameters showed to be potentially more sensitive than the parameters measured in the OECD 232 test in the case of sodium selenate contamination. For instance, both the number of eggs laid and the relative growth showed significant differences compared to the control group in lower concentrations than the juvenile number or mortality. In the groups treated with sodium selenite, the juvenile number was the most sensitive parameter. Based on our results, it can be stated that sodium selenite may be potentially more toxic to collembolans than sodium selenate. Lipid peroxidation was not initiated by selenium exposure. The glutathione redox system also did not activate either, which suggested that selenium toxicity in collembola is not a consequence of selenium-induced oxidative stress.

Evaluation of Juvenile Freshwater Mussel Sensitivity to Multiple Forms of Florpyrauxifen-Benzyl.

ProcellaCOR® (active ingredient [ai], florpyrauxifen-benzyl) is an aquatic herbicide registered for use in 2018 for managing invasive and nuisance macrophyte species. Registration studies evaluating its acute toxicity revealed a favorable environmental profile; however, prior to this study, no information existed on the toxicity of florpyrauxifen-benzyl to native freshwater mussels (Family Unionidae), one of the most sensitive and imperiled faunal groups globally. We followed standard acute (96h) toxicity test guidelines and exposed juvenile Fatmucket (Lampsilis siliquoidea) and Eastern Lampmussel (Lampsilis radiata) to the following formulations or compounds: ProcellaCOR SC and EC formulations, technical grade active ingredient (TGAI, florpyrauxifen-benzyl), and an analytical-grade sample of the weaker florpyrauxifen acid (FA). In all tests, the estimated median lethal concentrations to produce 50% mortality (LC50) were greater than the highest concentration tested of each formulation or compound. The no observable adverse effect concentrations (NOAEC, based on analytical recoveries measured at the highest concentration tested where no toxicity was observed) were TGAI = 26µg/L, FA = 100,000µg/L, ProcellaCOR® SC = 193µg ai/L ProcellaCOR® EC = 585µg ai/L and the NOAEC values for the registered commercial formulation products (ProcellaCOR® SC and ProcellaCOR® EC) were orders of magnitude greater (3.9× and 11.7×, respectively) than the maximum application rate (50µg/L). Our results show that the herbicide formulations and compounds tested were not acutely toxic to juveniles of these two species of freshwater mussels, indicating minimal risk of short-term exposure from florpyrauxifen-benzyl applications in the environment for aquatic weed control. However, potential chronic or sublethal effects remain uncharacterized and warrant additional investigation.

A pilot toxicology study of biogenic silver nanoparticles: in vivo by intraperitoneal and intravenous infusion routes in rats

Toxic effects of nanoparticles on human health are considerably increasing their worldwide recognition. Currently silver nanoparticles are being widely used in consumer medical products, due to its uniqueness in biomedical applications. Uptake of these particles via various administration routes can also lead to different toxic effects. In this study, we assessed the toxic effect of 11–75 nm ranged biogenic silver nanoparticles (Bio-AgNPs) on male wistar rats by using two different administration routes namely, intraperitoneal and intravenous routes. The three different concentrations, No Observable Adverse Effect Concentration (NOAEC), Inhibitory concentration (IC50) and Total lethal concentration (TLC) was appraised at the dose range of 97.64 to 132 µg/kg for both i/p and i/v routes. There is no considerable changes in hematological parameters in i/p and i/v routes on 14th and 28th day of observation, but the increase was trivial significant for platelet count at the dose of 97–105 µg/kg (IC50) for i/p route of injection. There is no remarkable adverse impact on liver, spleen and kidney were observed in IC50 and TLC treated group, when determined by biochemical and histopathological analysis both in i/p and i/v routes treated rats. This estimation confirms that, Bio-AgNPs are not going effect the human metabolic system.

Concentration-dependent alterations in gene expression induced by cadmium in Solanum lycopersicum.

Cadmium (Cd) toxicity in agricultural soil has received significant attention because of its higher transformation in the food chain and toxicity to humans. The aim of the present study was to develop sensitive and specific biomarkers for Cd stress. Therefore, transcriptional analyses were performed to investigate concentration-response characteristics of Cd responsive genes identified from a Solanum lycopersicum microarray. The results showed that the lowest observable adverse effect concentrations (LOAECs) of Cd to S. lycopersicum were 1mg/kg for seed germination, 8mg/kg for root dry weight, 8mg/kg for root elongation, and 8mg/kg for root morphology. Furthermore, the genes were differentially expressed even at the lowest Cd concentrations (0.5mg/kg), indicating that the detection of Cd in soil at the molecular level is a highly sensitive method. Cd in soil was positively correlated with the expression of the F-box protein PP2-B15 (r=0.809, p<0.01) and zinc transporter 4 (r=0.643, p<0.01), indicating that these two genes could be selected as indicators of soil Cd contamination.

Evaluating the teratogenicity of the selective ß3-adrenoceptor agonist, CL 316.243 hydrate by employing FETAX (frog embryo teratogenesis assay)

In this study, the frog embryo teratogenesis assay (FETAX – Xenopus) technique was employed to evaluate the potential teratogenicity of the selective ß-adrenoceptor (AR) agonist, CL 316.243. In this context, CL 316.243 was applied to the South African clawed frog (Xenopus laevis) embryos. The media containing the CL 316.24-exposed embryos were monitored and changed/replaced once every 24 hours. Using FETAX, we determined the minimum concentrations to inhibit growth (MCIG) for CL 316.243. The 96-hour no observable adverse effect concentration (NOAEC), the 96-hour lowest observable adverse effect concentration (LOAEC), the 96-hour EC50 (malformation) and the 96-hour LC50 (lethal concentration) for mortality and malformation could not be determined because the used concentrations did not affect viability or the presence of abnormalities. On the other hand, the MCIG of CL 316.243 was determined as 1 mg/L. Our results demonstrated that CL 316.243 administration was associated with no of teratogenic and toxic effects. However, from first concentration we used (1 to 5 mg/L) length of embryos reduced significantly (p < 0.001) when compared to control of Xenopus embryos. Further studies should be conducted with different concentrations in order to investigate the optimal concentrations for treating preterm labor with these substances.

Effect of Tulathromycin on Colonization Resistance, Antimicrobial Resistance, and Virulence of Human Gut Microbiota in Chemostats.

To evaluate microbiological safety of tulathromycin on human intestinal bacteria, tulathromycin (0, 0.1, 1, 10, and 100 μg/mL) was added into Chemostats. Before and after drug exposure, we monitored (1) population, SCFA products, antimicrobial resistance, and colonization resistance of gut microbiota, and (2) the antimicrobial resistance genes, transferability, virulent genes, pathogenicity of Enterococus faecalis. Results showed that low level of tulathromycin did not exhibit microbiological hazard on resistance selection and colonization resistance. However, high level of tulathromycin (10 and 100 μg/mL) may disturb colonization resistance of human gut microbiota and select antimicrobial resistant E. faecalis. Most of the selected resistant E. faecalis carried resistant gene of ermB, transferable element of Tn1545 and three virulence genes (esp, cylA, and ace). One of them (E. faecalis 143) was confirmed to have higher horizontal transfer risk and higher pathogenicity. The calculated no observable adverse effect concentration (NOAEC) and microbiological acceptable daily intake (mADI) in our study was 1 μg/mL and 14.66 μg/kg.bw/day, respectively.

Survey and Risk Assessment ofApis mellifera(Hymenoptera: Apidae) Exposure to Neonicotinoid Pesticides in Urban, Rural, and Agricultural Settings

A comparative assessment of apiaries in urban, rural, and agricultural areas was undertaken in 2013 and 2014 to examine potential honey bee colony exposure to neonicotinoid insecticides from pollen foraging. Apiaries ranged in size from one to hundreds of honey bee colonies, and included those operated by commercial, sideline (semicommercial), and hobbyist beekeepers. Residues in and on wax and beebread (stored pollen in the hive) were evaluated for the nitro-substituted neonicotinoid insecticides imidacloprid and its olefin metabolite and the active ingredients clothianidin, thiamethoxam, and dinotefuran. Beebread and comb wax collected from hives in agricultural landscapes were more likely to have detectable residues of thiamethoxam and clothianidin than that collected from hives in rural or urban areas (∼50% of samples vs. <10%). The maximum neonicotinoid residue detected in either wax or beebread was 3.9 ppb imidacloprid. A probabilistic risk assessment was conducted on the residues recovered from beebread in apiaries located in commercial, urban, and rural landscapes. The calculated risk quotient based on a dietary no observable adverse effect concentration (NOAEC) suggested low potential for negative effects on bee behavior or colony health.

Biomarker discovery and gene expression responses in Lycopersicon esculentum root exposed to lead

Gene expression analysis has shown particular promise for the identification of molecular biomarkers that can be used for further evaluation of potential toxicity of chemicals present in agricultural soil. In the study, we focused on the development of molecular markers to detect Pb toxicity in agricultural soil. Using the results obtained from microarray analysis, twelve Pb-responsive genes were selected and tested in different Pb concentrations to examine their concentration–response characteristics using real-time quantitative polymerase chain reaction (RT-qPCR). All the Pb treatments set in our study could generally induce the differential expression of the 12 genes, while the lowest observable adverse effect concentration (LOAEC) of Pb for seed germination, root elongation, biomass and structural modification derived from 1,297, 177, 177, and 1,297mgPb/kg soil, respectively, suggesting that the transcriptional approach was more sensitive than the traditional end points of death, growth, and morphology for the evaluation of Pb toxicity. The relative expression of glycoalkaloid metabolism 1 (P=−0.790), ethylene-responsive transcription factor ERF017 (P=−0.686) and CASP-like protein 4C2 (P=−0.652) demonstrates a dose-dependent response with Pb content in roots, implying that the three genes can be used as sensitive bioindicators of Pb stress in Lycopersicon esculentum.

Investigations of the Toxic Effect of Silver Nanoparticles on Mammalian Cell Lines

Silver nanoparticles are widely used for many applications. In this study silver nanoparticles have been tested for their toxic effect on fibroblasts (NIH‐3T3), on a human lung adenocarcinoma epithelial cell line (A‐549), on PC‐12‐cells, a rat adrenal pheochromocytoma cell line, and on HEP‐G2‐cells, a human hepatocellular carcinoma cell line. The viability of the cells cultivated with different concentrations of silver was determined by the MTT assay, a photometric method to determine cell metabolism. Dose‐response curves were extrapolated and IC50, total lethal concentration (TLC), and no observable adverse effect concentration (NOAEC) values were calculated for each cell line. As another approach, ECIS (electric‐cell‐substrate‐impedance‐sensing) an automated method to monitor cellular behavior in real‐time was applied to observe cells cultivated with silver nanoparticles. To identify the type of cell death the membrane integrity was analyzed by measurements of the lactate dehydrogenase releases and by determination of the caspase 3/7 activity. To ensure that the cytotoxic effect of silver nanoparticles is not traced back to the presence of Ag+ ions in the suspension, an Ag+ salt (AgNO3) has been examined at the same concentration of Ag+ present in the silver nanoparticle suspension that is assuming that the Ag particles are completely available as Ag+ ions.

Evaluating the Teratogenicity of Ritodrine and Nifedipine using a Frog Embryo Teratogenesis assay (FETAX)

The Frog Embryo Teratogenesis Assay—Xenopus (FETAX) was used to assess the teratogenic potential of two tocolytics. Embryos of the South African clawed frog, Xenopus laevis, were exposed to ritodrine or nifedipine. Exposure media were changed and monitored at 24-hour intervals. The 96-hour LC50 (Lethal concentration), the 96-hour EC50 (Malformation), and the No Observable Adverse Effect Concentrations (NOAEC) and the Lowest Observable Adverse Effect Concentration (LOAEC) for mortality, malformation and length were determined for each drug. Nifedipine was determined to be the more toxic and teratogenic than ritodrine, with a LC50 of 0.606 µg/L, an EC50 of 0.006 µg/L, and a teratogenicity Index (TI) value (LC50/EC50) of 101. On the other hand, the LC50 of ritodrine was 28.571 mg/L. In addition; the LC50, EC50 and TI values for nifedipine in the 5 mg/L ritodrine + nifedipine combination group were determined as 1.050 µg/L, 0.868 µg/L and 1.5 respectively. For ritodrine, the NOAEC and LOAEC values were determined as 2 mg/L and 4 mg/L, respectively. For the nifedipine and the ritodrine + nifedipine groups; while the LOAEC values of these groups were 0.0001 µg/L and 0.1 µg/L, respectively. NOAEC value couldn’t be determined. Our results demonstrated that nifedipine administration was associated with higher levels of teratogenic and toxic effects. However, the ritodrine + nifedipine combination form reduced the toxic and teratogenic effects of nifedipine on Xenopus embryos. Further studies should be conducted in order to investigate the optimal combination concentrations of these substances for the treatment of preterm labor.

Determining the effects of a mixture of an endocrine disrupting compound, 17α-ethinylestradiol, and ammonia on fathead minnow (Pimephales promelas) reproduction

Aquatic organisms are exposed to a multitude of contaminants and to fully understand the impact of multiple stressors on fish populations, we must first understand the mechanism of action for each toxicant and how the combined effects manifest at the level of the individual. 17α-ethinylestradiol (EE2) has been known to cause adverse reproductive effects including reduced fecundity and fertility, intersex and skewed sex ratios in fish by mimicking naturally produced estrogen at low concentrations. Ammonia can cause adverse reproductive and mortality effects in individual fish through effects or damage to the central nervous system. Both EE2 and ammonia are found in most municipal effluents in various concentrations. A flow-through diluter system was used to test the individual effects of these two contaminants at their respective no observable adverse effect concentration (NOAEC) as well as their combined effects on fathead minnow, (Pimephales promelas) reproduction in a mixture exposure. While neither contaminant nor their mixture altered reproduction in terms of fecundity, their mixture resulted in significant fathead minnow mortality during a 21d exposure. This study demonstrated the need to consider mixture effects when assessing risk for toxicity testing with multiple stressors.

Determining the Ecological Impacts of Organic Contaminants in Biosolids Using a High-Throughput Colorimetric Denitrification Assay: A Case Study with Antimicrobial Agents

Land application accounts for ∼ 50% of wastewater solid disposal in the United States. Still, little is known regarding the ecological impacts of nonregulated contaminants found in biosolids. Because of the myriad of contaminants, there is a need for a rapid, high-throughput method to evaluate their ecotoxicity. Herein, we developed a novel assay that measures denitrification inhibition in a model denitrifier, Paracoccus denitrificans Pd1222. Two common (triclosan and triclocarban) and four emerging (2,4,5 trichlorophenol, 2-benzyl-4-chlorophenol, 2-chloro-4-phenylphenol, and bis(5-chloro-2-hydroxyphenyl)methane) antimicrobial agents found in biosolids were analyzed. Overall, the assay was reproducible and measured impacts on denitrification over 3 orders of magnitude exposure. The lowest observable adverse effect concentrations (LOAECs) were 1.04 μM for triclosan, 3.17 μM for triclocarban, 0.372 μM for bis-(5-chloro-2-hydroxyphenyl)methane, 4.89 μM for 2-chloro-4-phenyl phenol, 45.7 μM for 2-benzyl-4-chorophenol, and 50.6 μM for 2,4,5-trichlorophenol. Compared with gene expression and cell viability based methods, the denitrification assay was more sensitive and resulted in lower LOAECs. The increased sensitivity, low cost, and high-throughput adaptability make this method an attractive alternative for meeting the initial testing regulatory framework for the Federal Insecticide, Fungicide, and Rodenticide Act, and recommended for the Toxic Substances Control Act, in determining the ecotoxicity of biosolids-derived emerging contaminants.

Biofunctional quantum dots as fluorescence probe for cell-specific targeting

We describe here the synthesis, characterization, bioconjugation, and application of water-soluble thioglycolic acid TGA-capped CdTe/CdS quantum dots (TGA-QDs) for targeted cellular imaging. Anti-human epidermal growth factor receptor 2 (HER2) antibodies were conjugated to TGA-QDs to target HER2-overexpressing cancer cells. TGA-QDs and TGA-QDs/anti-HER2 bioconjugates were characterized by fluorescence and UV–Vis spectroscopy, X-ray diffraction (XRD), hydrodynamic sizing, electron microscopy, and gel electrophoresis. TGA-QDs and TGA-QDs/anti-HER2 were incubated with cells to examine cytotoxicity, targeting efficiency, and cellular localization. The cytotoxicity of particles was measured using an MTT assay and the no observable adverse effect concentration (NOAEC), 50% inhibitory concentration (IC50), and total lethal concentration (TLC) were calculated. To evaluate localization and targeting efficiency of TGA-QDs with or without antibodies, fluorescence microscopy and flow cytometry were performed. Our results indicate that antibody-conjugated TGA-QDs are well-suited for targeted cellular imaging studies.

In vitro cytotoxicity and morphological assessment of smoke from polymer combustion in human lung derived cells (A549)

The application of polymer and composites in building and modern transport interiors raises concerns of potential health hazards during combustion. Cytotoxicity and morphological assessment of smoke from polymer combustion in human lung derived cells (A549) has been investigated. A laboratory scale vertical tube furnace was used for the generation of combustion products. A range of materials used in the building and transport industry including high density-polyethylene (HDPE), polypropylene (PP), polycarbonate (PC), and polyvinyl chloride (PVC), fiberglass reinforced polymers (FRPs), and melamine faced plywood (MFP) were studied. The exposure of combustion toxicants to human lung cells (A549) at the air/liquid interface was acquired using a Harvard Navicyte Chamber. Cytotoxic effects on human cells were assessed based on cell viability using a selected in vitro cytotoxicity assays, including NRU (neutral red uptake) and ATP (adenosine triphosphate). Morphological assessment on the effects of combustion products in human lung cells from selected materials including PVC, FRP and MFP was assessed using scanning electron microscopy (SEM). The volatile organic compounds from thermal decomposition products were identified using ATD-GCMS (Automatic Thermal Desorption Gas Chromatography Mass Spectrometry). NOAEC (No Observable Adverse Effect Concentration), IC(10) (10% inhibitory concentration), IC(50) (50% inhibitory concentration), and TLC (Total Lethal Concentration) values (mg/l) were generated. The following toxicity ranking was observed from the most toxic material to the least toxic using the NRU assay: PVC>PP>HDPE>PC >FRP-10>MFP>FRP-16; and the ATP assay: PVC>HDPE>PP>FRP-10>FRP-16>MFP>PC. The method described here could potentially be an alternative to current fire toxicity standards.

PAMAM-functionalized water soluble quantum dots for cancer cell targeting

Herein, the phase-transfer reaction of quantum dots (QDs) with amine-terminated polyamidoamine (PAMAM) dendrimers with controllable ligand molar ratios was achieved. The unique properties of PAMAM allowed us to build up structurally and electrostatically stabilized water soluble QD complexes. Synthesized conjugates were characterized in terms of fluorescence and UV-Vis profiles, hydrodynamic size, number of surface dendrimer groups, and stability. Cytotoxic effects of conjugates for MCF-7, A-549 and HEP-G2 cancer cells were assessed based on cell viability using MTT assay. Cytotoxicity results were expressed as no observable adverse effect concentration (NOAEC), 50% inhibitory concentration (IC50) and total lethal concentration (TLC) values (μM). Furthermore, HER2 receptor-mediated targeting efficiency of antibody labelled P/QDs conjugates was evaluated by successful staining of MCF-7 cells with bioconjugates. Uniquely, effective cell internalization was achieved with well-characterized antibody coupled P/QDs in contrast to antibody free P/QDs conjugates. Fluorescence microscopy images demonstrated that the designed PAMAM-derivatized QDs nanoparticles show great potential in the areas of cellular imaging and targeted therapy.

An alternative method for in vitro fire smoke toxicity assessment of polymers and composites using human lung cells

AbstractAn alternative method for in vitro fire smoke toxicity assessment of polymers and composites using human lung cells has been investigated. A range of building and train interiors including polyethylene (PE), polypropylene (PP), polycarbonate (PC), polymethyl methachrylate (PMMA), polyvinyl chloride (PVC), fiberglass‐reinforced polymer (FRP), and melamine‐faced plywood (MFP) were studied. The exposure of combustion toxicants to human lung cells (A549) at the air/liquid interface was acquired using a Harvard Navicyte Chamber. Cytotoxic effects on human cells were assessed based on cell viability using the MTS assay (Promega). Cytotoxicity results were expressed as no observable adverse effect concentration (NOAEC), 10% inhibitory concentration (IC10), 50% inhibitory concentration (IC50), and total lethal concentration (TLC) values (mg/l). Mass loss data and toxic product yield were also determined. Results suggested that PVC (IC50 1.99 mg/l) was the most toxic materials followed by PP, FRP‐16, PC, PMMA, FRP‐10, PE, and melamine plywood. Some materials revealed to be more toxic under flaming combustion (PP, PC, FRP‐16, and FRP‐10), while others (PVC, PMMA, PE, and melamine plywood) appeared more toxic under non‐flaming combustion. The method developed can be used to screen the toxicity of materials which would be important information in building and mass transport material selection. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Workplace exposures equivalent to no or low observable adverse effect concentrations in animals: Step by step approach

Workplace exposures equivalent to no or low observable adverse effect concentrations in animals: Step by step approach

Predicting hormesis in mixtures.

Figure 1. Selected concentration–response relationships for the inhibition of root length of Lactuca sativa. The figures, adapted from Belz et al. (2008), illustrate how both the dose range and the size of the maximal response is approximately proportional to the mixture ratio of 50:50%, both for mixtures between 2 hormetic compounds (a) and between a hormetic and a nonhormetic compound (b). L e a rn e d D ico u se PREDICTING HORMESIS IN MIXTURES

Toxicity reference values for mink exposed to 2,3,7,8-tetrachlodibenzo- p-dioxin (TCDD) equivalents (TEQs)

Dietary and tissue residue-based toxicity reference values (TRVs) were derived for mink from the published results of studies in which mink were exposed to polychlorinated dibenzo- p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), or related compounds. Because the primary mechanism of toxic action at the least concentration for these compounds is related to activation of the aryl hydrocarbon receptor (AhR), TRVs were described on the basis of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) equivalents (TEQ). Each published study was critically reviewed for its usefulness in deriving a TRV based on the following criteria: (1) close relatedness of the test species to the wildlife receptor of concern (only mink studies were reviewed in this paper); (2) chronic duration of exposure which included sensitive life stages to evaluate potential developmental and reproductive effects; (3) measurement of ecologically relevant endpoints; (4) availability of congener-specific data to calculate TEQ concentrations; and (5) minimal impact of co-contaminants. Dietary TRVs for mink exposed to TEQ ranged from 12.1 to 56.6 ng TEQ/kg feed (wet weight) for the no observable adverse effect level (NOAEL) and from 50.4 to 242 ng TEQ/kg feed (wet weight) for the lowest observable adverse effect level (LOAEL). TRVs based on tissue residue concentrations ranged from 50.2 to 77.8 ng TEQ/kg liver (wet weight) for the no observable adverse effect concentration (NOAEC) and the value was 189 ng TEQ/kg liver (wet weight) for the lowest observable adverse effect concentration (LOAEC). Selection of a TRV should be based on studies of compounds that are most similar to those at a site of interest. In particular, it was determined that the effects of PCDFs could not be accurately predicted from the use of TEQ-based TRVs developed from studies of PCDDs or PCBs. Risk assessors should be aware that exceedance of these TRVs would not necessarily be expected to lead to ecologically relevant adverse effects because of the inherently conservative assumptions made in the TRV derivation process.

RISK ASSESSMENT OF GREAT HORNED OWLS (BUBO VIRGINIANUS) EXPOSED TO POLYCHLORINATED BIPHENYLS AND DDT ALONG THE KALAMAZOO RIVER, MICHIGAN, USA

The great horned owl (GHO; Bubo virginianus) was used in a multiple lines of evidence study of polychlorinated biphenyls (PCBs) and p,p'-dichlorodiphenyltrichloroethane (DDT) exposures at the Kalamazoo River Superfund Site (KRSS), Kalamazoo, Michigan, USA. The study examined risks from total PCBs, including 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQWorld Health Organization [WHO]-Avian Toxicity Equivalency Factor [TEF]), and total DDTs (sum of DDT, dichlorodiphenyldichloroethylene [DDE], and dichlorodiphenyldichloroethane [DDD]; sigmaDDT) by measuring concentrations in eggs and nestling blood plasma in two regions of the KRSS (upper, lower) and an upstream reference area (RA). An ecological risk assessment compared concentrations of the contaminants of concern (COCs) in eggs or plasma to toxicity reference values. Productivity and relative abundance measures for KRSS GHOs were compared with other GHO populations. Egg shell thickness was measured to assess effects of p,p'-DDE. The concentrations of PCBs in eggs were as great as 4.7 x 10(2) and 4.0 x 10(4) ng PCB/g, wet weight at the RA and combined KRSS sites, respectively. Egg TEQ(WHO-Avian) calculated from aryl hydrocarbon receptor-active PCB congeners and WHO TEFs ranged to 8.0 and 1.9 x 10(2) pg TEQ(WHO-Avian)/g, (wet wt) at the RA and combined KRSS, respectively. Egg sigmaDDT concentrations were as great as 4.2 x 10(2) and 5.0 x 10(3) ng sigmaDDT/g (wet wt) at the RA and combined KRSS, respectively. Hazard quotients (HQs) for the upper 95% confidence interval (UCI) (geometric mean) and least observable adverse effect concentration (LOAEC) for COCs in eggs were < or = 1.0 for all sites. Hazard quotient values based on the no observable adverse effect concentration (NOAEC) 95% UCI in eggs were < or = 1.0, except at the LKRSS (PCB HQ = 3.1; TEQ(WHO-Avian) HQ = 1.3). Productivity and relative abundance measures indicated no population level effects in the UKRSS.