ISSN:0730-7268    

DOI:10.1002/etc.5620141001

出版商:Wiley Periodicals, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractOctamethylcyclotetrasiloxane (OMCTS, or D4) is a highly volatile, cyclic silicone that is an important intermediate in the synthesis of polydimethylsiloxanes and other higher‐molecular‐weight silicones. As a category of chemicals, silicones have generated substantial scientific and regulatory interest over the last few years. OMCTS, one of the first silicones considered for regulatory review, was recommended for testing in the 15th Report of the Interagency Testing Committee (ITC) in 1984 based on its high volume of production, alleged presence in aquatic environments, and the general lack of environmental fate and effects information for this type of compound. As a result, the environmental effects and fate of OMCTS have been extensively evaluated in a series of laboratory toxicity and environmental fate studies, fate modeling studies, and field monitoring studies. Most of these studies were conducted as part of a negotiated consent order (CO) under Section 4 of the Toxic Substances Control Act (TSCA). Applying the principles of ecological risk assessment (ERA) to the OMCTS program, the current paper presents the problem‐formulation phase of the ERA process including stressor characteristics, identification of the ecosystem potentially at risk, and development of a conceptual model. In addition, the planning phase with interactions among the industry representatives, the risk assessors, and the risk managers are discussed. OMCTS was one of the first chemicals to reach the RM1 (risk management) level of regulatory analysis under TSCA, which resulted in a determination that no additional data was needed. Application of ERA principles in this program were instrumental in this favorable determin

ISSN:0730-7268    

DOI:10.1002/etc.5620141002

出版商:Wiley Periodicals, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe toxicity of octamethylcyclotetrasiloxane (OMCTS) to representative freshwater and marine fish and invertebrates was investigated. Testing procedures followed Toxic Substance Control Act (TSCA) guidelines with chemical‐specific adaptations as presented in the OMCTS Testing Consent Order (Docket OPTS‐42071A). The physicochemical properties and behavior of OMCTS (i.e., high volatility, low water solubility) precluded the use of conventional experimental practices and exposure systems. Procedures and systems developed during these investigations provided a mechanism that produced exposure levels equal to the maximum achievable (i.e., “functional”) solubility of OMCTS in natural dilution waters. The toxicant delivery systems and exposure chambers were designed to minimize volatilization by elimination of the air/water interface. The flow‐through systems maintained consistent exposure concentrations and adhered to U.S. Environmental Protection Agency (EPA) Guideline test performance criteria. The “functional” water solubility of OMCTS in freshwater and seawater ranged from 14 to 30 μg/L and from 6.0 to 9.0 μg/L, respectively. Functional water solubility appeared to vary slightly with test conditions and dilution water characteristics. Continuous exposures of 2 to 93 d were conducted during these investigations with daphnids (Daphnia magna), rainbow trout (Oncorhynchus mykiss), mysids (Mysidopsis bahia), and sheepshead minnow (Cyprinodon variegatus). The rainbow trout was determined to be the most sensitive species to OMCTS (14‐d LC50 = 10 μg/L). At levels equal to the functional water solubility, OMCTS was not acutely toxic toD. magna, mysids, or sheepshead minnow. The survival ofD. magnawas reduced by 16%, relative to the control organisms, after 21‐d exposures to 15 μg/L OMCTS; exposure to 7.9 μg/L OMCTS or less had no effect on daphnid survival or reproduction. No toxicity was observed at the highest concentration tested in a 93‐d exposure of rainbow trout early life stages. The no‐observed‐effect concentration for this study was 4.4 μg/L, the same as determined i

ISSN:0730-7268    

DOI:10.1002/etc.5620141003

出版商:Wiley Periodicals, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractTwo aqueous exposures of fathead minnows (Pimephales promelas) were conducted to determine the bioconcentration factor (BCF) for [14C]octamethylcyclotetrasiloxane (OMCTS). The high volatility, high sorptive capacity, and low water solubility of OMCTS required that the testing be conducted in a novel, totally enclosed, flow‐through exposure system that prevented the volatilization of the test substance. In a preliminary study, fish were continuously exposed to OMCTS at a concentration of approximately 0.5 μg/L for 6 d. In the definitive study, fish were exposed for 28 d at approximately 0.3 μg/L. In each case, OMCTS exposures were followed by a 14‐d depuration period. Water concentrations and fish residues were measured periodically in both studies. Data from the 6‐d study resulted in a maximum measured BCF of 7,000. Model calculations based on data from the 6‐d exposure phase predicted a steady‐state BCF of 10,000 after 19 d of exposure. The definitive study resulted in a steady‐state measured BCF of 12,400 after 28 d of exposure. Model calculations based on the measured data from the 28‐d exposure phase provided an estimated BCF of 13,400. The OMCTS bioconcentration factors could be accurately estimated from the data produced during a 6‐d continuous exposure. The use of innovative test systems was key to the development of useful bioc

ISSN:0730-7268    

DOI:10.1002/etc.5620141004

出版商:Wiley Periodicals, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractAmbient concentrations of the volatile octamethylcyclotetrasiloxane (OMCTS) in natural waters were predicted using two environmental‐fate analyses: an atmospheric model and a sewage treatment plant model. The atmospheric‐fate analysis utilizes a completely mixed model of the troposphere where degradation occurs by hydroxyl radical oxidation. The treatment plant analysis incorporates removal mechanisms of biodegradation, volatilization, and adsorption. The treatment train consisted of primary clarifiers followed by secondary treatment using an activated sludge process. Two estimates of influent concentration were used in the model, one based on total consumption data and the other based on measured sludge data. Because of the widely varying estimates, a sampling program was undertaken and the data were used for final effluent estimates. Measured influent OMCTS concentrations of several wastewater treatment plants indicated that less than 5% of the consumable OMCTS is received by treatment plants. From the atmospheric analysis, the predicted OMCTS concentration in the ambient water in equilibrium with the atmosphere is from 10−5to 10−8μg/L. Using measured influent concentrations, the sewage treatment plant analysis predicted average effluent concentrations of 0.39 to 0.66 μg/L. Both analyses predicted concentrations that were less than the lowest chronic no‐observed‐effect concentration (4.4 μg/L), thus providing no significant aq

ISSN:0730-7268    

DOI:10.1002/etc.5620141005

出版商:Wiley Periodicals, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThis paper presents an aquatic ecological risk assessment, including an aquatic effects assessment, an exposure assessment, and a characterization of risk to aquatic organisms. In a number of acute and chronic studies with several aquatic species, octamethylcyclotetrasiloxane (OMCTS) toxicity was observed, but only after extended, continuous exposures of 7 to 14 d; survival was the only biological end point affected. The symptoms of toxicity observed were highly consistent with narcosis as the mechanism of action. For all aquatic toxicity testing, the lowest NOEC was 4.4 μg/L for rainbow trout in both 14‐d and 90‐d tests. The physicochemical characteristics of OMCTS (low solubility, high Kow, and very high Henry's law constant) indicate that the water concentrations should be low and transient, consistent with results of environmental‐fate studies that demonstrate that OMCTS moves rapidly out of water. The primary route of release of OMCTS to the environment is associated with use in personal‐care products, which would potentially result in release to air and water via public sewer systems. Environmental‐fate models predict low concentrations of OMCTS in air and water. Monitoring studies indicate mean measured concentrations of OMCTS in sewage treatment plant effluents of 0.06 to 0.41 μg/L. Assuming 50% bioavailability of OMCTS and a dilution factor of three, calculated mean concentrations of dissolved OMCTS in surface waters range from 0.01 to 0.068 μg/L. Comparison of the lowest no‐observed‐effect concentration (NOEC) from all toxicity testing with this predicted range of surface water concentrations indicates a conservative margin of safety to 64 to 444 for aquatic organisms. Rapid volatilization and additional dilution in most aquatic environments will increase this margin of safety even further. Based on all available evidence, the risk of OMCTS to aquatic ecosystems is character

ISSN:0730-7268    

DOI:10.1002/etc.5620141006

出版商:Wiley Periodicals, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractA statistical analysis was done of the relationship between hydrophobicity and bioconcentration parameters (uptake and elimination rate constants and bioconcentration factor) predicted by the diffusive mass‐transfer (DMT) concept of bioconcentration developed previously. We employed polychlorinated biphenyls and benzenes (PCB/zs) as model compounds and the octanol/water partition coefficient as hydrophobicity parameter. We conclude that the model is consistent with the data. Subsequently, we applied the DMT concept to a set of preliminary bioconcentration data for surfactants using the critical micelle concentration (CMC) as hydrophobicity parameter. The obtained relationships qualitatively agree with the DMT concept, indicating that hydrophobicity is of great influence on surfactant bioconcentration. Finally, we investigated the hydrophobicity‐bioconcentration relationships of surfactants and PCB/zs using aqueous solubility as common hydrophobicity parameter and found the relationships between the bioconcentration parameters and hydrophobicity to agree with the DMT concept. These findings are based on total radiolabel data. Therefore, they need to be confirmed using compound‐specific surfactant bioconcentration

ISSN:0730-7268    

DOI:10.1002/etc.5620141007

出版商:Wiley Periodicals, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe acute toxicity of cadmium, copper, and mercury to the benthic epiphytic foraminiferanPararotalia spinigera(Le Calvez) was investigated using seven different vital cytophysiological and cytochemical methods. The ability to enzymatically hydrolyze the fluorogenic substrates fluorescein diacetate or fluorescein dibutyrate was the most sensitive method of LC50 value determination. The LC50 (24‐h) values for cadmium, copper, and mercury determined by this assay with fluorescein diacetate was 0.56, 1.4, and 0.07 μM, respectively. The content of seaweed‐derived dissolved organic carbon (DOC), measured by absorbance at 436 nm, produced a dramatic increase of LC50 values for the heavy metals in a dose‐dependent manner. “Intact” epiphytic foraminifera attached to seaweeds are less sensitive to acute toxicity of cadmium, copper, and mercury than are “detached

ISSN:0730-7268    

DOI:10.1002/etc.5620141008

出版商:Wiley Periodicals, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractCoelomocytes of the earthwormLumbricus terrestriscaused significant spontaneous allogeneic cytotoxicity in a 24‐h trypan blue assay, but not in an assay using lactate dehydrogenase (LDH) release. Allogeneic cytotoxicity assays using cells from worms exposed to polychlorinated biphenyls (PCBs) suggest that PCBs can suppress a natural killing (NK‐like) reaction. The implications of this work are twofold: understanding the evolution of natural killing (NK‐like) activity and providing preliminary information on how spontaneous killing, a component of cellular immunity, may be compromised by pollu

ISSN:0730-7268    

DOI:10.1002/etc.5620141009

出版商:Wiley Periodicals, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractIn a two‐factorial experiment, sulfur dioxide alone at concentration of 131 μg/m3over long exposures or flyash from either coal or oil combustion alone applied onto cucumber (Cucumis sativusL.) foliage causes no visible injury. However, if both flyash and sulfur dioxide were presented simultaneously, a specific mosaic‐chlorosis symptom developed on leaves. A synergistic effect was thus demonstrated. Histopathology of the mosaic‐chlorosis symptom was studied. An unusual pattern of tissue abnormally initiated from the collapse of the anticlinal cell walls of the upper epidermal cells and progressed along cell walls into mesophyll tissues. Cellular injury at the lower spongy tissues typical of that caused by SO2was also observed. A significant elevation of sulfate‐sulfur in the leaves treated with a combination of SO2and flyash was demonstrated. Significant interactions between the two factors were found for both injury and sulfur chemistry. This suggests that flyash deposits on the leaf surface play a catalytic role in oxidizing atmospheric sulfur dioxide continuously to form sulfuric acid (H2SO4) in situ. This acid could infiltrate into mesophyll damage cells and tissues

ISSN:0730-7268    

DOI:10.1002/etc.5620141010

出版商:Wiley Periodicals, Inc.    

年代:1995

数据来源: WILEY