Toxicological evaluation of methyl tertiary butyl ether (MTBE): Testing performed under TSCA consent agreement

MTBE is a colorless, relatively volatile liquid that has found widespread use as an octane‐enhancing gasoline additive. In 1987, the Environmental Protection Agency's (EPA) Interagency Testing Committee identified MTBE for priority testing consideration based on large production volume, potential widespread exposure, and limited data on chronic health effects. In response, the industry formed the MTBE Health Effects Testing Task Force, which in 1988 signed a Consent Agreement with the EPA requiring the task force member companies to perform toxicological testing on MTBE.

The testing program, which began in the second quarter of 1988, consists of a full complement of short‐ and long‐term tests. The testing completed to date includes genotoxicity (in vivo bone marrow cytogenetics and Drosophila sex‐linked recessive lethal assays), developmental toxicity, acute and subchronic neurotoxicity (motor activity, functional observation battery, and neuropathology), subchronic toxicity, reproductive/fertility effects, and pharmacokinetic studies. There is also an ongoing oncogenicity study in rats and mice. The final report for this chronic study is expected at the end of 1992. The total cost for the program is approximately $3.75 million, which is funded by the 11 Task Force member companies based on market share.

These studies were sponsored by the MTBE Health Effects Testing Task Force, Oxygenated Fuels Association, Washington, D.C.     

The pH-independent effect of aluminum on cultures of phytoplankton from an acidic Wisconsin lake

Negative correlations between aluminum and planktonic algal abundance have been reported in acidic lakes. Natural assemblages of phytoplankton from a low-pH, low-Al lake (Franklin Lake, WI) were grown in semi-continuous cultures consisting of four treatments at pH 5.7 with 0.0, 50, 100, and 200 μg Al L⁻¹ and one treatment at pH 4.7 with no Al added. Asterionella ralfsii var. americana (a common diatom plankter in acidic lakes) grew well at both pH 4.7 and 5.7 when no Al was added but declined in all other treatments and so may be useful as an indicator of acidic, low monomeric-Al conditions. Other common plankters that showed this pattern included: Arthrodesmus indentatus, Ar. octocornus, Ar. quiriferus, Staurastrum arachne var. curvatum, S. longipes var. contractum, and S. pentacerum. Common taxa showing no toxic effects of Al were Dinobryon bavaricum, Peridinium limbatum, Stenokalyx monilifera, Elaktothrix sp. and Oedogonium sp. We hypothesize that metal toxicity as a pulse at spring snowmelt could dramatically change algal succession in moderately acidic lakes. The experimental results agreed well with field observations. These types of experiments are useful for predicting the responses of natural phytoplankton communities to increases in Al concentration.     

Toxicity of sewage-contaminated sediment cores to Macrocystis pyrifera (Laminariales,Phaeophyta) gametophytes determined by digital image analysis

Macrocystis pyrifera gametophytes were exposed in batch culture to varying mass concentrations of buried, sewage-contaminated, historically discharged sediment that had been sampled from two sites off Palos Verdes Peninsula, California. Significant gametophytic vegetative growth inhibition was detected in six days, using digital image analysis at sediment loadings ranging from 0.15 to 14.5 g in 500 mL nutrient-enriched seawater. Inhibition declined at low sediment loadings and increased at high loadings as cultures aged. Sediments corresponding to the historic emissions peak taken 2 km from the Joint Water Pollution Control Plant outfall inhibited vegetative growth more than did sediments sampled 13 km distant. Analysis showed elevated aqueous Cd(II), Cr(II) and p,p-DDE concentrations in high sediment-loading culture medium. Inhibition by Zn(II) alone was observed at similar concentrations in other experiments, but synergism or antagonism by other toxicants remains possible.     

ZINC ADSORPTION AND TRANSPORT BY CHLAMYDOMONAS VARUIABILIS AND SCENEDESMUS SUBSPICATUS (CHLOROPHYCEAE) GROWN IN SEMICONTINUOUS CULTURE1

The amount of zinc adsorbed onto the cell surface of the unicellular green algae Scenedesmus subspicatus Hodat and Chlamydomonas variabilis Dangeard was operationally defined by extraction with EDTA; it was a function of the concentration of free ionic zinc remaining in the growth medium, rather than that of the total (free plus complexed) zinc concentration, and could be described by Langmuir isotherms. Conditional adsorption equilibrium constants for zinc were 0.123 and 0.039 L ·μmol^?1 for S. subspicatus and C. variabilis, respectively. A portion of the zinc adsorbed onto C. variabilis was released into solution after 1 h of contact with the metal, providing a possible tolerance mechanism for this alga; the division rate of C. variabilis was not altered by up to 12 μmol Zn²⁺· L^?1, although the cell yield obtained during the stationary phase was significantly decreased. The amount of transported or cellular zinc, for both algal species, was operationally defined as the zinc remaining with the cell after EDTA-extraction; it was a linear function of the free ionic zinc concentration remaining in solution, suggesting that the zinc transported into the cell was not derived from the total adsorbed fraction, although the latter may contain some zinc originating from specific sites leading to zinc transport.     

Inhibition of Axoplasmic Transport in the Optic System by Kainic Acid

Axoplasmic transport along the optic axons was studied after intraocular injections of kainic acid (KA). Transport of labeled material did not initiate from the eye when KA was injected simultaneously with the protein precursor [3H]proline. When KA was injected after axoplasmic transport of labeled proteins had begun, no additional radioactive material moved out of the retinal ganglion cells. However, the labeled material already present in the optic nerve at the time of KA injection continued to move, and accumulated at the nerve endings. Although KA reduces the incorporation of precursor, this effect of KA on axoplasmic transport appears to be more than a consequence of inhibition on precursor uptake or protein synthesis. Recovery from this KA action began 6 h after exposure to KA and was about 50% recovered by 36 h. The extent of the recovery remained at this level for as long as a week, which suggested a partial recovery of the ganglion cells. A second exposure to KA after the inner plexiform layer had virtually disappeared was as effective as the first exposure in preventing the appearance of transported protein in the optic nerve, suggesting a direct action of KA on the ganglion cells. We interpreted the results to indicate that KA interferes with the initiation phase of axoplasmic transport in ganglion cells and this effect is partially reversible.     

Brain Regional Distribution of Glutamic Acid Decarboxylase, Choline Acetyltransferase, and Acetylcholinesterase in the Rat: Effects of Chronic Manganese Chloride Administration after Two Years

Abstract: Rats were treated chronically with manganese chloride from conception onward for a period of over 2 years in order to study the effects of manganese and aging on the activities of glutamic acid decarboxylase (GAD), choline acetyltransferase (ChAT), and acetylcholinesterase (AChE) in hypothalamus, cerebellum, pons and medulla, striatum, midbrain, and cerebral cortex (which included the hippocampus). Manganese-treated 2-month-old and 24- to 28-month-old rats and age-matched controls were studied. In control rats during aging the activities of GAD decreased in hypothalamus (19%), pons and medulla (28%), and midbrain (22%) whereas the activities of AChE decreased in all regions (20–48%), particularly in the striatum (44–48%). Changes in ChAT activities in aging were observed only in one region—a decrease (23%) in the striatum. Life-long treatment with manganese appeared to abolish partially the decreases in aging in AChE activities in hypothalamus, cerebellum and striatum, and striatal ChAT activity. Manganese treatment also seemed to abolish the age-related decreases in GAD activities, since GAD activities in various brain regions of manganese-treated senescent rats were not significantly different from those of control young rats. These results are discussed in relation to other metabolic changes associated with aging and manganese toxicity.     

Effect of soil Cd addition on germination of native plant species

Soil Cd addition was found to adversely affect germination ofAndropogon scoparius, Monarda fistulosa, andRudbeckia hirta. Rudbeckia germination was found to be most sensitive to soil Cd addition andAndropogon germination most tolerant (b=–.0001). Soil cadmium concentrations sufficient to reduce germination by 25% were calculated to be 30 and 46 g Cd/g soil forRudbeckia andAndropogon respectively.Contribution from Purdue University Agricultural Experiment Station, West Lafayette, Indiana 47907. AES Journal No. 7594. This work was supported by federal funds from the National Science Foundation — RANN Program.     

Oxygen consumption by Campylobacter sputorum subspecies Bubulus with formate as substrate

The kinetics of oxygen utilization by the microaerophile Campylobacter sputorum subspecies bubulus was studied. With formate as substrate two enzyme systems were found to be responsible for electron transfer between formate and oxygen. In the case of lactate oxidation one enzyme system could account for the activity measured. One of the formateoxidizing systems possessed a high affinity for oxygen [K _m(O₂)=approx. 4M O₂]. From inhibitor studies it was concluded that a respiratory chain was involved in its activity. Respiration by this system must be responsible for proton translocation and electron transport-linked phosphorylation at formate oxidation. The other enzyme system had an extremely low affinity for oxygen [K _m (O₂)=approx. 1 mM O₂]. It was tentatively identified as the H₂O₂-producing formate oxidase previously found in C. sputorum. The H₂O₂ production by this enzyme is implicated in an explanation of the microaerophilic nature of C. sputorum. Sensitivity of formate dehydrogenase to H₂O₂ was demonstrated. The influence of the formate concentration on aerobic formate oxidation was determined. The pH- and temperature dependencies of oxygen uptake with formate as substrate were examined at airsaturation and at a low dissolved oxygen tension.Abbreviations TL medium tryptose-lactate medium - TF medium tryptose-formate medium - HQNO 2-n-heptyl-4-hydroxyquinoline N-oxide - SHAM salicylhydroxamic acid - DCPIP 2,6-dichlorophenolindophenol     

Cystinotic and normal fibroblasts: Differential susceptibility to cysteine toxicity in vitro

Summary Extracellular cysteine concentrations between 0.5 and 2.5 mM resulted in death of normal but not cystinotic cells grown in Eagle's minimal essential medium containing supplemental fetal bovine serum and antibiotics. Differential cell survival was determined by viable cell counting using Trypan Blue dye exclusion. In cocultivation experiments of [³H]thymidine-labelled cystinotic fibroblasts with nonradioactive normal fibroblasts, autoradiography confirmed the selective survival of cystinotic cells in medium containing 1 mM cysteine. At this concentration of 1 mM cysteine, intracellular cystine content increased slightly in surviving normal cells but not in cystinotic cells, which normally contain a high level of intracellular cystine. This comparative resistance of cystinotic fibroblasts to elevated extracellular cysteine concentrations forms the basis for an in vitro selective system for these mutant human cells. Further exploration of this resistance phenomenon may well expand the understanding of the molecular defect in cystinotic cells.     

The effect of copper on glutathione metabolism in human leukocytes

Leukocytes incubated with Cu(II) showed a decrease in both glutathione reductase activity and reduced glutathione content. The glucose 6-phosphate dehydrogenase activity under the same conditions was not affected. Serum albumin added to mixtures prevented the loss of enzyme activity, whiled-penicillamine andl-histidine had little effect. Prior oxidation of the cell-reduced glutathione did not diminish the enzyme inhibitory action of Cu(II). The amount of regeneration of reduced glutathione in leukocytes previously treated with diamide to oxidize their reduced glutathione was a function of Cu(II) concentration in the media. No evidence was obtained that elevated serum ceruloplasmin levels in rabbits, nor incubation of leukocytes in vitro with ceruloplasmin, affect leukocyte glutathione reductase activity. It was proposed that the major mechanism by which copper affects glutathione metabolism in leukocytes is by inhibition of glutathione reductase.