Vol. 10 No. 6 December 1990


Table of Contents

I. Veterinary Notes: Cattle
II. Analysis of L-Tryptophan for the Etiology of Eosinophilia-Myalgia Syndrome
III. Ames Assails Animal Tests, Calls for Rethinking Their Utility
IV. OMB Blasts Use of Conservatisms in Risk Assessments
V. Risk Assessment Not Well Served by Bioassays, Workshop Told
VI. Carbon Monoxide Levels in Indoor Tractor-Pull Events - Manitoba, Canada
VII. Continuing Education Requirement for Qualified Applicator Certificate Holders
VIII. Cleaning Up Toxics at Home


This newsletter marks the end of a very interesting year in the annals of environmental toxicology and also public policy relating to the environment. If next year is anything like this last one, it will not be dull! The most interesting story to me this year is the one centering around the eosinophilia-myalgia syndrome (EMS). There have been many clues (the latest are printed in this issue), and in the early part of next year we should know a lot more about its etiology. Stay tuned.

This is our annual subscription issue and a renewal form is attached, and I am sure you will want to use it. Next year we will guarantee at least four issues, and hopefully publish six. As always, we welcome topic suggestions from readers, and we also welcome submissions for inclusion. One sign that this newsletter is actually being read in some places is that it is now being indexed in AGRICOLA, the National Agricultural Library bibliographic database. Thank you all for your support.

I. Veterinary Notes


Poison hemlock (Conium maculatum) toxicosis was confirmed by the Toxicology Laboratory (Davis) as the cause of increased salivation, ataxia and occasional deaths in 2 herds consuming hay bought from the same source. The hay contained 60% Poison hemlock. Toxic metabolites of the plant were detected in the urine from cattle on both farms using an experimental technique.

NOTE: This finding by Dr. Frank Gayley and his crew is of great importance since it has been previously thought that poison hemlock loses its toxicity when dried in hay. In certain areas of California, alfalfa fields may be heavily infested with hemlock during the spring. If any readers have encountered any problems with suspected hemlock toxicity, please contact us. Thank you.

Datisca glomerata ("Durango root") toxicosis caused diarrhea and lethargy prior to death in 5 heifers from a beef operation in the coastal range foothills. The plant, from the rumen contents, was submitted for identification to the Toxicology Laboratory (Davis) by the practitioner. This plant has been demonstrated to cause toxicosis experimentally and there have been past reports of toxicosis in cattle in the coastal and sierra foothills during dry years.

Reference: California Veterinary Diagnostic Laboratory System: Lab Notes, Vol. 3, No. 3, August 1990.

II. Analysis of L-Tryptophan for the Etiology of Eosinophilia-Myalgia Syndrome

Eosinophilia-myalgia syndrome (EMS) has been associated with consumption of L-tryptophan-containing products (LTCPs) and most strongly associated with consumption of LTCPs produced by one manufacturer. Epidemiologic and laboratory investigations have suggested that the implicated LTCPs were contaminated. To further examine this hypothesis, CDC and the Food and Drug Administration (FDA) conducted additional laboratory studies. This report summarizes preliminary data that indicate that implicated LTCPs were contaminated with the di-tryptophan aminal of acetaldehyde (DTAA).

High-resolution fast-atom bombardment mass spectrometry determined the exact mass of peak 97 to be 434.2020 corresponding to a molecular formula of C24H26N4O4, indicating that peak 97 contained two tryptophan molecules and an additional C2H2. These data suggested that peak 97 was the DTAA (Figure 1A).

With LT as a standard, the concentration of peak 97 was estimated at 0.01% in a typical case-associated LT lot. Scientists at the implicated manufacturer independently arrived at the same proposed structure. Confirmation of this structure by synthesizing DTAA is in progress. In addition to peaks 97, 100, and 200, ongoing investigation is directed at 1-methyl- 1,2,3,4-tetrahydro-B-carboline-3-carboxylic acid (MTCA) and bacitracin, detected in LT lots from the implicated manufacturer. MTCA could be produced from the breakdown of DTAA or independently formed.

The figure below shows the first proposed structure of peak 97 and a further refinement based on more testing. Initial studies were hampered by having only minute amounts of peak 97 to analyze. Now that an animal model has been identified, studies are underway to see if this compound is really the one causing the disease.

Editorial Note: The epidemiologic association of peak 97 and any other particular compound with EMS indicates that these compounds may either be the causative agent(s) or marker(s) for a different, as yet unidentified, causative agent in case- associated LT lots. Based on an average daily dose of 2 g of LT for a 70-kg person and a 30-day delay before onset of EMS, the total dose of peak 97 is approximately 90 ug/kg. The toxic properties of the aminals are not well defined; however, the suspected decomposition products, the B-carbolines, exhibit a variety of biologic properties.

The full definition of biologic and toxic effects of the contaminants can be determined only in an animal model for EMS. A joint National Institute of Mental Health/National Institutes of Health/FDA/CDC study has recently reproduced EMS-like changes in rats. Synthesizing these contaminants and testing them in the new rat model may help to clarify their relationship to the etiology and pathogenesis of EMS. Continuing studies include analyzing additional LT lots, identifying and synthesizing contaminants, and attempting to associate changes in the manufacturing process with these contaminants.

Reference: MMWR, Vol. 39/No. 34, August 31, 1990.

MMWR, Vol. 39/No. 43, November 2, 1990.

III. Ames Assails Animal Tests, Calls for Rethinking Their Utility

"Animal cancer tests are conducted at near toxic doses (the maximum tolerated dose (MTD)) of the test chemical for long periods of time, which can cause chronic mitogenesis," and can be thought of as a "chronic wounding, which is known to be both a promoter of carcinogenesis in animals and a risk factor for cancer in humans," Drs. Bruce N. Ames and Lois Swirsky Gold of the University of California (Berkeley) pointed out.

Therefore, they said, "a high percentage of all chemicals might be expected to be carcinogenic at chronic, near toxic doses, and this is exactly what is found. About half of all chemicals tested chronically at the MTD are carcinogens."

They pointed out that this holds for both synthetic chemicals (212/350) and natural chemicals (37/77), while for mold toxins tested at the MTD, 11 out of 16 are rodent carcinogens.

Ames and Gold also contrasted the consumption of natural pesticides in the diet, about 1500 mg per person per day, with the average intake per day of residues of 100 synthetic pesticides, 0.09 mg per person per day.

Additionally, they said, thousands of pyrolysis products are produced in cooking food. Estimating that dietary intake of these products is roughly 2000 mg per person per day, Ames and Gold continued: "Few of these have been tested; for example, of 826 volatile chemicals that have been identified in roasted coffee, only 21 have been tested chronically, and 16 are rodent carcinogens; caffeic acid, a non-volatile carcinogen, is also present. A cup of coffee contains at least 10 mg (40 ppm) of rodent carcinogens (mostly caffeic acid, catechol, furfural, hydrogen peroxide, and hydroquinone)."

They called for comparing the "very low exposures to pesticide residues or other synthetic chemicals ... to the enormous background of natural substances. Pesticide residues (or water pollution) must be put in the context of the enormous background of natural substances, and there is no convincing evidence from either epidemiology or toxicology that they are ofinterest as causes of human cancer," Ames and Gold urged, adding: "Minimizing pollution is a separate issue, and is clearly desirable for reasons other than effects on public health."

They pointed out that "humans are well buffered against toxicity at low doses from both manmade and natural chemicals. Given the high proportion of carcinogens among those natural chemicals tested, human exposure to rodent carcinogens is far more common than generally thought; however, at the low doses of most human exposures (where cell-killing and mitogenesis do not occur), the hazards may be much lower than is commonly assumed and often will be zero." Ames and Gold added:

"Without studies of the mechanisms of carcinogenesis, the fact that a chemical is a carcinogen at the MTD in rodents provides no information about low-dose risk to humans. We must increase research to identify more major cancer risks," Ames and Gold urged, "and to better understand the hormonal determinants of breast cancer, the viral determinants of cervical cancer, and the dietary determinants of stomach and colon cancer. In this context," they concluded, "the most important contribution that animal studies can offer is insight into carcinogenesis mechanisms and into the complex natural world in which we live."

Reference: Food Chemical News, Vol. 32, No. 27, September 3, 1990.

IV. OMB Blasts Use of Conservatisms in Risk Assessments

In an overview section of its Regulatory Program of the U.S. Government, the Office of Management and Budget sharply criticized use of conservatisms in risk assessments.

"Conservatism in risk assessment distorts the regulatory priorities of the federal government, directing societal resources to reduce what are often trivial carcinogenic risks while failing to address more substantial threats to life and health. Distortions are probably most severe in the area of cancer-risk assessment, because many conservative models and assumptions were developed specifically for estimating upper bounds for these risks. Risk assessment methods with similar conservative biases are less common elsewhere, particularly in those areas where real-world data are available, or where the mechanism by which injury or illness occurs is better understood."

OMB said "the continued reliance on conservative (worst- case) assumptions distorts risk assessment, yielding estimates that may overstate likely risks by several orders of magnitude." Stating that many risk assessments are based on bioassays utilizing sensitive rodent species dosed at extremely high levels, the agency said: "Conservative statistical models are used to predict low-dose human health risks, based on the assumption that human biological response mimics that observed in laboratory animals. Worst-case assumptions concerning actual human exposure are commonly used instead of empirical data,further exaggerating risk levels."

Stating that "the choice of an appropriate margin of safety should remain the province of responsible risk-management officials, and should not be preempted through biased risk assessments," OMB said "estimates of risk often fail to acknowledge uncertainty, nor do they present the extent to which conservative assumptions overstate likely risks."

It alleged that "analyses of risk-management alternatives routinely ignore these uncertainties and treat the resulting upper-bound estimates as reliable guides to the likely consequences of regulatory action, and decisionmakers and the general public often incorrectly infer a level of scientific precision and accuracy in the risk-assessment process that does not exist."

"To the extent that policymakers and the public fail to understand the magnitude of the margin of safety embedded in quantitative risk assessments, policy choices are distorted from the course that would have been selected if decisionmakers had been better informed of the actual risks. Ironically, these policy decisions may actually increase total societal risk. Too much attention is focused on relatively small hazards that have been exaggerated by conservative risk assessments, leaving alone larger risks that have been estimated using unbiased procedures."

Noting that the Office of Science and Technology Policy and the Environmental Protection Agency have recommended "that relevant animal studies should be considered irrespective of whether they indicate a positive relationship," OMB stated that, "In practice, however, studies that demonstrate a statistically significant positive relationship routinely receive more weight than studies that indicate no relationship at all."

As an example, the agency said that daminozide and its metabolite 1,1-dimethylhydrazine were classified as "probably" human carcinogens. OMB stated: "Each of these classifications was based on a single positive animal bioassay. Overcoming such a classification requires, at a minimum, two `essentially identical' studies showing no such relationship." In the case of Alar, OMB said, a "more stringent test was apparently applied," noting that "three high-quality negative studies showed no significant effects," but "these studies appear to have received little or no weight in the classification decision."

Reference: Food Chemical News, Vol. 32, No. 26, August 27, 1990.

NOTE: The continuing debate about the relevance of chronic animal testing to levels of chemical exposure of humans is further presented in the next article.

V. Risk Assessment Not Well Served by Bioassays, Workshop Told

The classic bioassay in which rodents are fed toxic chemicals at "maximum tolerated dose" (MTD) was not designed for risk assessment, Dr. Michael A. Gallo, Robert Wood Johnson Medical School in New Jersey, declared at an MTD workshop Sept. 6 sponsored by the National Research Council's Committee on Risk Assessment Methodology (CRAM).

Responding to remarks from the audience by an Environmental Protection Agency pesticide regulator, Gallo commented that "hazard identification and risk assessment are different processes," adding, "The bioassay has made your life difficult; CRAM needs to fill in the gaps so that regulators can do their jobs better."

Dr. Eugene McConnell, a toxicology consultant based in Raleigh, NC, called the MTD a "concept, not an authoritative reality," and an "impossible target to hit, in most cases." He noted that doses above or below the MTD may be difficult to interpret, thereby making regulatory decisions difficult.

Responding to McConnell, Dr. John Emmerson, Eli Lilly & Co., agreed that selection of the MTD is difficult, and has not changed much since the concept emerged in the 1950s, yet he urged perseverance despite difficulties. "Good science is poorly served by convenience," he declared in reply to critics who would abandon bioassays or test at lower doses. Emmerson suggested that the "classical definition" of MTD could be improved by stipulating that a dose be selected "with reasonable assurance that pharmacokinetics and physiological responses be proportionate and qualitatively similar to those of other animals."

Dr. Ian Munro, Canadian Centre for Toxicology, commented, "Our real problem (with the MTD) is how to interpret the results, not in designing the experiment." He said the highest dose should be one that: "(1) is adequate to characterize the chronic toxicity of the chemical yet does not induce overt toxicity leading to untimely death from effects that would preclude being at risk from tumor development; (2) does not induce gross disturbances in organ function (as determined by clinical and biochemical methods) which would produce a physiological state incompatible with normal clinical function; (3) is chosen with a full understanding of the pharmacokinetics and metabolic profile in relation to dose so that one knows in advance that rate- limiting mechanisms or qualitative changes in metabolism may be at play in tumor development; (4) does not exceed a level which produces alterations in nutrient intake or utilization; such doses will be of limited relevance to humans."

Discussing correlations between the MTD and measures of carcinogenic potency, Dr. Daniel Krewski, Health and Welfare Canada, reviewed evidence suggesting a close relationship between the maximum dose tested and the dose at which 50% of animals develop tumors above the background rate for cancer (TD50). "Carcinogenic potency has also been shown to be somewhat correlated with both acute toxicity and mutagenicity, both of which are important factors in neoplastic change," Krewski continued, adding that other scientists "have demonstrated a strong correlation between a composite index based on toxicity and mutagenicity and carcinogenic potency as measured by the TD50. These results suggest that data on toxicity and mutagenicity may be combined to narrow down the uncertainty in the carcinogenic potential of chemicals not yet subjected to the long-term carcinogen bioassay."

University of California researcher Dr. Bruce Ames, reviewed his case against the MTD, which he has called a "chronic wounding" of test animals that promotes cell division and is thus carcinogenic in and of itself. Asked if naturally-occurring pesticides should be bred out of plants, Ames replied that it could be done, but he would not advocate such a step. "I'm not worried about carcinogens in plants," he declared, adding that "human cancer will be sorted out by epidemiologists," and suspect compounds will then be tested with animals.

Responding to Ames, Gallo issued a plea for greater research into oncogene activation and other cancer mechanisms, declaring, "Sophisticated biometry can't improve crude biology."

Reference: Food Chemical News, Vol. 32, No. 28, September 10, 1990.

VI. Carbon Monoxide Levels in Indoor Tractor-Pull Events - Manitoba, Canada

Carbon monoxide (CO) and other noxious gases produced by internal combustion devices are health hazards in enclosed spaces. In facilities such as underground garages and indoor arenas, CO is a particular concern because of its rapid toxic effects and potentially high concentrations. In February and November 1988, the City of Winnipeg Health Department (WHD), Manitoba, Canada, conducted surveys of two tractor-pull events in an indoor 15,000-seat arena to determine levels of CO. During the November event, an attempt was made to mitigate CO levels. This report summarizes findings from the two surveys.

A "tractor" is a truck or other vehicle modified to look like a farm tractor (e.g., large rear wheels and smaller front wheels) and powered by a variety of units (e.g., aircraft turbines and supercharged car engines). A tractor-pull event lasts approximately 21 hrs and involves 25 individual pulls.

Previous monitoring of CO in the arena's seating area during full-occupancy hockey games indicated CO levels of 0-10 ppm; an ice-edger and an ice-resurfacing machine, both of which emit CO, were used several times each during each game. The WHD's recommended indoor guideline levels are 33 ppm for a 1-hr exposure and 18 ppm for an 8-hr exposure.

At the February event, measurements indicated an average level of 68 ppm at the start (8 p.m.) of the first of 25 pulls; however, several tractors had been running their engines before the first pull. By 10:30 p.m. (the end of the competition), the CO level had increased to 262 ppm. In general, CO levels were uniform throughout the seating area. During this event, however, the ventilation system had not been operating at full capacity, tractors had been allowed to run their engines before the event, and large doors to the arena's ground floor had been closed.

During the November event, measures to decrease CO levels included reducing the number of pulls to 24, expanding the event by 2 hrs to permit decay in the CO level, and opening ventilating louvres in the arena roof. WHD inspectors used the same measuring apparatus to take readings at the same locations as in the February event. CO levels at the beginning of the event averaged 77.5 ppm and increased to 435.7 ppm by the event's close.

This evaluation indicated that the control measures were not effective in reducing CO levels. Participants did not want to retrofit their tractors with pollution-control devices because this would decrease the horsepower of the tractors. Therefore, WHD officials required that appropriate ventilation improvements be implemented before further tractor-pull events could be permitted in the arena. However, because one evaluation concluded that the costs to implement the ventilation improvements were prohibitive, a tractor-pull scheduled for February 1989 was cancelled, and no further such events are to be held in the arena.

Editorial Note: Because CO poisoning is frequently not suspected in persons suffering from CO intoxication, morbidity from CO poisoning is difficult to estimate. Unintentional poisoning has resulted from exposure to high levels of CO from automobiles, ice-resurfacing machines, fork lifts, recreational vehicles, and kerosene heaters and other fuel-burning household devices. Current Environmental Protection Agency outdoor air quality standards permit 9 ppm CO as an 8-hr average and 35 ppm as a maximum 1-hr level. In the United States, there are no indoor air standards for CO. Japan has established a guideline of 10 ppm.

CO is a colorless, odorless, nonirritating gas produced by incomplete combustion of fuels and present in all exhaust and smoke, including cigarette smoke. CO is toxic because 1) it avidly binds to hemoglobin to form carboxyhemoglobin (COHb), which reduces the oxygen-carrying capacity of blood, and 2) it inhibits cytochrome oxidase within mitochondria, thereby poisoning cellular respiration. The latter effect is increased in cases in which tissue hypoxia already exists and in cases of chronic CO intoxication. The risk for toxicity is proportionate to metabolic rate, exercise, prolonged exposure, and high altitude. Populations at risk for CO poisoning include the elderly, the poor (during the winter heating season), pregnant women (because of risk to the fetus), and persons with heart disease, lung disease, or anemia.

Symptoms of mild to moderate CO poisoning are nonspecific; the most commonly reported symptoms are headache, dizziness, weakness, nausea, confusion, shortness of breath, and visual problems. In addition, CO exposure can cause or exacerbate cardiac abnormalities (e.g., angina), and low COHb levels can cause complex ventricular arrhythmias. Occult CO poisoning should be suspected when these symptoms occur in two or more persons who have a history of sharing enclosed quarters. A blood COHb level >2% in nonsmokers or >10% in smokers confirms CO exposure; levels of >30% are commonly associated with severe symptoms and may result in neuropsychiatric sequelae. Because COHb levels may not reflect tissue levels, they should be interpreted cautiously -- especially in cases of chronic CO intoxication. Home or worksite measurement of ambient CO levels may be necessary to establish the diagnosis in cases of chronic low-level exposure.

Preventive measures include regular automobile maintenance; routine cleaning and adequate venting of gas-fired stoves, furnaces, and appliances; and adequate ventilation and pollution controls during indoor events such as tractor-pulls.

Reference: MMWR, Vol. 39/No. 41, October 19, 1990.

VII. Continuing Education Requirement for Qualified Applicator Certificate Holders

California law requires accredited continuing education instruction for pesticide applicators prior to certificate renewal. During each two year certificate period each certificate holder is required to obtain at least 20 hours of continuing education. Detailed information on the requirement has been sent to certificate holders by CDFA and copies are available from your local County Agricultural Commissioner.

Continuing education is provided by many agencies and organizations; hundreds of hours are offered in every part of the state every year. A schedule of Future Pest Management Conferences and Meetings is published by Robert Kennedy, Hartnell College Pest Management. This schedule is available to UC personnel free of charge. You can have your name added to the mailing list by sending your request for the pesticide training schedule on your official UC stationary to: Pest Management Computer, P.O. Box 80016, Salinas, CA 93012.

Attendance at accredited meetings should be recorded. Signing the sign up sheet at meetings will assure that your attendance is recorded. You do not have to be a licensed PCA to take advantage of this service.

Course instructors can get an annual accounting of the ethnic makeup of the meeting participants from the Pest Management Computer.

M.W. Stimmann

VIII. Cleaning Up Toxics at Home

Cleaning Up Toxics at Home (presented by the League of Women Voters of California Education Fund) was recently broadcast on television in the Bay Area. Dr. Ali Harivandi made a copy of the program and its companion program titled Cleaning Up Toxics in Business. We have viewed them and highly recommend them for your own viewing and public education programs. If you are interested, a copy (VHS) is available on loan through our office or we will arrange to make a copy for you if you provide a videotape cassette.

Art Craigmill
Extension Toxicologist
UC Davis

Mike Stimmann
Statewide Pesticide Coordinator
UC Davis