Styrene is a colorless or yellowish liquid, which is usually characterized by a penetrating, sweet odor (ATSDR…, 1995). Its chemical formula isC8H8 (NTP…). It is generally synthetic, having been produced in the United States since the 1920s by catalytic dehydrogenation of ethylbenzene (IARC…, 1994). Styrene does not easily dissolve in water. Styrene has a flash point of 31.1 degrees Celsius, a freezing point of –33 degrees Celsius, and a molecular weight of 104.16 (NTP…). Low levels of Styrene appear naturally in foods such as fruits, vegetables, nuts and meats (ATSDR…, 1995).

In an economic sense, Styrene is one of the world’s most important commercial chemicals. In 1993, worldwide production capacity was 17.8 million tons (Cruzan et al…, 2001), and is produced by many major chemical corporations such as Dow, Shell, and Chevron (Cruzan et al…, 2001). It is commonly used in the reinforced plastics industry for use in fiberglass-reinforced polyester, boat hulls and automobile parts (ATSDR…, 1995). It is also used in the production of insulation, Styrene-butadiene rubber and latex, carpet backing, unsaturated Polystyrene and Acrylonitrile-butadiene-styrene resins, and industrial adhesives, although it’s most widely known use is as Polystyrene for food packaging (ATSDR…, 1995).

How does Styrene interact with the environment?

Styrene, when released into the air, breaks down entirely within one to two days, and it will quickly evaporate in shallow waters and soils (ATSDR…, 1995). Styrene has a half life of just a few days when in surface water, but in groundwater, Styrene has a half life of anywhere between six weeks to seven and a half months (ATSDR…, 1995).

Styrene does not generally stick to soils or sediments and is easily broken down by bacteria in soils and water (ATSDR…, 1995). Because of the relative speed in which Styrene eliminates itself from soils and surface water, it is not commonly found in animals, and does not seem to be a candidate for significant biomagnification (ATSDR…, 1995).

How is Styrene disposed of?

Styrene is released into the environment as an industrial pollutant, basically waste in the manufacture of Styrene-based products. It also enters the environment through the disposal of Styrene products and packaging into the waste stream (ATSDR…, 1995). Styrene itself is disposed of by incineration at temperatures above 2000 degrees Fahrenheit, in a specialized high temperature chemical disposal facility (NTP…).

What are the Laws on Styrene?

As of March 1998, The American Conference of Governmental Industrial Hygienists’ set standard for general occupational exposure was 20 ppm, a level that is not generally associated with health concerns (Brown et al, 2000). As of July 1996, OSHA’s set standard for high occupational exposure was 100 ppm, with an absolute limit at 200 ppm (Brown et al, 2000). Health problems have been reported in humans at levels as low as 50 ppm (Sherrington, 2001). OSHA’s standard allows for concentrations as high as 600 ppm for a period of no longer then five minutes (Brown et al, 2000).

How does Styrene impact local communities?

There is a definite growing concern as to the impact of the industrial output of Styrene and other chemicals on neighboring communities. During the past three decades, chemical emissions of varying types have been reduced, but in some areas, such as Akwesasne, New York, Styrene is still a problem because of its economic importance to large companies with local factories such as General Motors, ALCOA, and Reynolds Metals (Akwesasne…, 2000). Grassroots organizations have formed throughout the country in places like Akwesasne to form lobbing power to reduce the emissions of Styrene and other chemicals into their communities (Akwesasne…, 2000). However, as of yet this movement, particularly the factions surrounding less glamorous chemicals such as Styrene, have yet to gain momentum (Akwesasne…, 2000).

How does Styrene effect human health?

A 2000 report by the University of London shows that there is actually little current reliable evidence to show that Styrene is extremely dangerous to humans (Brown et al, 2000). Studies, while hindered by lack of data, have alluded to the lack of toxicity of Styrene to humans at natural or occupational exposure (IARC…, 1994). However, there should be caution in classifying Styrene as entirely safe for humans, as the lack of concrete information as to its toxicity (particularly cancer data) is not proof of its safety. The University report also outlines the need for continuing unbiased research, and that it is still clear that Styrene is a potentially fatal toxicant with ill effects at moderate contact levels (Brown at el, 2000). Direct contact in liquid form causes eye and skin irritation (NTP…), and should be avoided in all situations. It is recommended that anyone who becomes in contact with liquid Styrene should see a physician immediately, regardless of the presence of symptoms (NTP…). Inhalation exposure has been known most commonly to affect the nervous system, and can cause short term physiological effects such as depression, concentration problems, intoxication, and muscle weakness, while Styrene is in the system (ATSDR…, 1995). There have been individual cases of styrene exposure at occupational levels and above causing headaches, intoxication (Sherrington, 2001), and damage to the olfactory nerves (NTP…). Long term effects are debatable, but there is evidence to show that permanent liver or nervous system damage can result from prolonged exposure at above occupational levels (Brown et al, 2000).

There is some evidence to say specifically what Styrene will not do in terms of human toxicology. Studies have shown that Styrene is not a reproductive or developmental toxicant (Brown, et al, 2000). Studies have also shown that there is little risk that Styrene is genotoxic (Brown et al, 2000, NTP…). There is less certainty, however, as to whether or not Styrene has an effect on human chromosomes, because the studies that exist contradict each other (Brown et al, 2000).

The possible carcinogenic properties of Styrene are in constant question. Styrene has been known to cause cancer in mice, but only at extremely high levels, and occupational studies have suggested that no significant causation can be established, because of the lack of proper exposure data and isolation in such studies from other occupational toxicants.

Case Studies

A review of occupational studies; Styrene as a possible carcinogen

Since the 1970s, a number of occupational exposure studies to Styrene have been conducted by various companies and independent organizations (Brown, et al, 2000). These studies were most presumably conducted under different procedures at different times with different biases present. The assumption is made that because the conclusions offered by each are similar if not identical, the variance, in essence, reinforces the conclusion of each. The collective message and the individual results of these studies are, however, to be taken with caution, as specific data for each is lacking.

In a European multinational study of 40,000 workers in the reinforced plastics industry, a non-significant increase in cancer-related death was shown with relation to Styrene exposure. However, there was a significant relation to intensity of exposure as well as years since first exposure and the risk of developing lymphatic or haematopoietic cancer. No relation was found between cumulative exposure and the same risk of cancer (IARC…, 1994).

A separate study was conducted in Denmark using 12,800 male workers from the European study plus an additional 24,000 workers (all 36,600 from Denmark) with a lower probability of styrene exposure. Results were identical to the multinational study (Styrene…, 1994). In the United States, a large study was conducted of the reinforced plastics industry. In this study, there was no increase whatsoever in lymphatic or haematopoietic cancer in the general results, but a non-significant increase was seen at levels of high exposure (IARC…, 1994).
Further studies, one from the United States and one from the United Kingdom, have shown a non-significant increase in lymphatic or haematopoietic cancer cases. In the study from the United Kingdom, a considerably smaller study, there was reportedly a lack of information on exposure (IARC…, 1994).

A few studies from the United States have suggested an significant increase in lymphatic or haematopoietic cancer related to Styrene exposure, noting that, just as in the European multinational study, no relation was seen between cumulative exposure and cancer risk. What these studies say about the carcinogenic properties of Styrene, however, is in question given the studies’ reporting a lack of detailed exposure data (IARC…, 1994), a problem that has seemed to surface in Styrene exposure studies given that the use of styrene is often accompanied by other chemicals in equal or larger amounts. As a result, accurate exposure data is only available in the reinforced plastics industry, where Styrene use is high and usually isolated from other chemicals (Brown et al, 2000).

In general, occupational exposure studies are less then complete. The nature of these studies is demographic. While they serve as an indicator as to the real world impact of the chemical being studied, they tend to rationalize it’s continued use even if the chemical is potentially harmful or cancer-causing. In the case of Styrene, there is generally low occupational exposure, resulting in “non-significant” demographic cancer rates. Evidence shows that risk of cancer from Styrene exposure is increased with intensity to exposure and years since first exposure (IARC…, 1994), and in at least one study mentioned, that increase is significant. The resulting perception of Styrene as a possible carcinogen is one of confusion and doubt.

Mice (and industry scientists)

In 2001, Chemical industry scientist/consultant George Cruzan from the firm ToxWorks, along with scientists from chemical companies Chevron (Janette R. Cushman), Rohm + Hass (Larry S. Andrews), Shell Canada (Geoffrey C. Granville), Dow (Keith A. Johnson), and BP Amoco (Christopher Bevan), as well as Chemical industry research scientists from Huntingdon Life Sciences (Colin J. Hardy, Derek W. Coombs, Pamela A. Mullins) and Research Pathology Services (W. Ray Brown), published their study on the toxicity of Styrene in mice in the Journal of Applied Toxicology. The study involved exposing five groups of 70 male and 70 female four week old CD-1 mice to styrene vapor at five levels of concentration (0 [control], 20, 40, 80, and 160 ppm) for six hours a day five days a week (presumably to simulate a work week) for either 98 weeks for females, or 104 weeks for males. The authors describe the reasoning for conducting the study as an update to a similar study performed in the 1970s that was deemed inadequate and inappropriate for use in assessing the human health hazard of Styrene. The intended use of this study was not specifically outlined by the authors, however, it may be inferred that this study would be used to assess the human health hazard of and perhaps human health limits to Styrene, given the source of the report.

The mice were separated into five groups of 70 male and 70 female mice based on the level of exposure they received (group one: 0 ppm, group two: 20 ppm, group three: 40 ppm, group four: 80 ppm, and group five: 160 ppm). Prior to the study, the animals, classified as VAF (virus antibody free) CD-1 mice, were subjected to hematological and serological evaluation. No abnormalities were found. The mice were each fed an equal ratio of carbohydrates (88.5%), proteins (8.5%), soybean oil (0.5%) and dietary supplements (2.5%), The drinking water of the mice was analyzed every six months.

The mice from groups two through five were placed, by group, into 4.23m2 inhalation chambers, for six hours a day for five days a week. During this time, they were constantly exposed to Styrene vapor at a level that depended on which group they were in. Group one, the control group, was placed in an identical inhalation chamber for the identical amount of time, but was not exposed to Styrene. When not in the inhalation chambers, the mice were kept separated, each in their own plastic cage.

During the study, the mice were observed individually twice daily (once during placement and once during removal from the chambers). On weekends, the mice were observed during one period, en masse. Body weight was measured every week for the first 13 weeks, and then once every four weeks afterward. Before the study, halfway through the study, and one week before the end of the study, the eyes of the mice were examined. Blood and urine were collected on five occasions for hematological evaluation. At weeks 52 and 78, a pre-selected group of 10 males and 10 females from each group were killed and examined. At the end of the study, all of the surviving animals were killed and examined.

The study reports that Styrene had no effect of the survival of the male mice. The study also shows a surprising positive correlation between the exposure level of the female mice and their survival rate. The female control group showed a 54 percent survival rate at week 98 (the final week), whereas the group which was exposed to Styrene at a level of 160 ppm showed a 72 percent survival rate. Two of the female mice from group five (160 ppm) died in the first two weeks of the study, however, the end survival data suggests to the authors that there is a “slight dose-related increase in the survival of female mice” (Cruzan et al, 2001). Mice from groups four and five (80 and 160 ppm) gained weight at a slightly lower rate then the other groups. There was a loss in olfactory nerve fibers in mice exposed to levels at or higher then 40 ppm. There was an increase in benign lung tumors in male mice exposed to levels at or higher then 40 ppm, and a similar increase in female mice in all of the groups except the control group The increase in malignant lung tumors for female mice at levels of 160 ppm was significantly higher then the control group.

Saturation of metabolism within specific organs was not determined in this study, however, the conclusion of the study proposes that there were no adverse effects outside of the lung tumors, without clarifying that that portion discussion was confined to only the possible carcinogenic properties of Styrene. The authors offer no causation link between exposure to Styrene at 160 ppm and the 18 percent survival increase in female mice (but do say that it is “dose-related”), nor do they entertain any notion of testing anomalies or error. The authors, in their discussion, also repeatedly point out that susceptibility to Styrene is much higher in mice then in rats, according to a similar study of rats. The authors draw the conclusion that the metabolism of Styrene that causes tumors in mice is unique to mice, applying the rational to humans. The study denies, without being accused, that Styrene has any chromosomal or carcinogenic effect on humans, referring anecdotally to conflicting studies of human workers exposed to Styrene. The report, for no reason, uses the EPA Carcinogen Risk Assessment Guidelines to prove that because Styrene has only been proven (so far) to cause malignant tumors in one organ of one species, and so it is not a carcinogen. The study does not test other species and does not discuss the conclusions of other studies that do, by not doing so the authors take the EPA Guidelines out of context.

Perhaps because of the employment status of the authors, the wording of the study, particularly the discussion and conclusion, as very biased. In particular, it ignores certain assumptions that the data clearly suggests and fails to describe certain anomalies in the study, using and bending the data as seen fit. There was a 6 percent drop in survival rate of male mice exposed to Styrene at 160 ppm from the control group, with a small sample size of 50 male mice (the 20 that were killed from each group at weeks 52 and 78 were not included in the final results). The study states that there was no dose-related effect on male survival. Using this as a criteria, the female mice, whose survival rate at 160 ppm was an insignificant 4 percent higher then the male mice at the same level of exposure, were reported to have a “dose-related” increase in survival, due to the fact that nearly half of the female control group died.

This type of research does not promote the study of toxicology. The procedure itself was valid, however, the researchers irresponsibly prepared and presented their findings. The sample size was manipulated and was arguably too small to begin with, leaving the authors room for interpretation. The researchers were biased and the data was repeatedly manipulated. The final hypotheses of the authors were nothing more then ways to make the data fit their predisposed model.

Some Conclusions

Because of the “fair trial” that Styrene, and other chemicals with questionable impact, have received, there is risk of environmental and human health consequences. The prevailing perception of potentially dangerous chemicals in the developed world is one where a risk must become a tragedy, and then a demographically significant tragedy (the cynic proposes that it must furthermore become a economic tragedy) before it can be taken seriously. As of January 2001, Styrene is not listed as a known human carcinogen by the National Institute for Occupational Safety and Health (or NIOSH) (National Institute…, 2001). The listing of known carcinogens by NIOSH is done so that a chemical is only listed when it is in some way in contact with the American people, and absolute proof is given by exposure data that the chemical does increase the risk of cancer in humans. This list is updated biennially to make sure that chemicals are not listed when doubt is given to their possible carcinogenic properties. For example, Saccharin, for decades a publicly controversial artificial sweetener, was removed from the most recent list because, while it had been proven to cause cancer in rats, there was “less convincing evidence” that it causes cancer in mice (National Institute…, 2001), or humans for that matter.

Styrene was submitted for inclusion to NIOSH’s list of known carcinogens in 1991 (National Institute…, 2001) but was not considered for inclusion due to lack of evidence, and no formal tests have been ordered by NIOSH. NIOSH is currently awaiting results from studies authored by the chemical industry.

This guide entry recommends caution with the production and use of Styrene. The risks associated with the chemical are largely confined to the occupational realm, and those risks are perceived to be small, however, there must be care taken when dealing with an unknown. The current laws for Styrene are adequate, however, enforcement and worker knowledge are of the utmost importance. The accepted exposure rates should not be seen similarly to the current concept of an automobile speed limit, meaning the average amount, not the maximum as it should be. The regulation limits on Styrene exposure, and indeed other, more hazardous chemicals, must be placed on high priority, and severe penalties should be issued to companies who even accidentally and without incident violate the standard. In addition, every worker who is at remote risk to styrene exposure must fully comprehend the risks and be able to know and participate in the policies that effect that worker’s health. This could be done through a rigorous campaign to update worker training procedures in the industry.

While the overall impact of Styrene is essentially low to moderate in comparison to far more dangerous chemicals used by the chemical industry, the warning level is still high, because Styrene is an example of how progress can be halted by well planned confusion. The procedure for implementing the first steps toward a progressive environmental policy on Styrene are being hindered by repeated whispers, and furthermore, cries, from the chemical industry that Styrene has not just an insignificant impact of humans, but none whatsoever. This is clearly false. The data, as incomplete as it is, suggests that styrene does effect the functions of living beings, including humans, in a malignant way.

The context of chemical studies is usually demographic, which, despite being practical, can miss the point entirely. Even though studies that showed little significant increase in cancer rates compared to the general populous, there is general acknowledgement that the cancer rates increase to a significant level when reducing the subject population to those who have had increased exposure.

The discussion shouldn’t be as to weather or not human beings can take being sprayed with poisons for 40 hours a week and come out mostly whole. The discussion should be how can the industry prevent (or be forced to prevent) exposing thousands of workers, and indeed the population at large, to entirely unknown future consequences until there are no unknowns, and the course is clear. The cynic proposes that it is all about money, and in a fringe case such as Styrene, the cynic might be right.

Resources

Akwesasne Task Force on the Environment (2000). ATFE web site. Retrieved March 11, 2002 from http://www.slic.com/atfe/atfe.htm

ATSDR: Agency for Toxic Substances and Disease Registry. (September 1995). ToxFAQs for Styrene. Retrieved Feburary 22, 2002 from http://www.atsdr.cdc.gov/tfacts53.html

Brown, Nigel A., Lamb, James C., et al. (2000). A review of the developmental and reproductive toxicity of Styrene. Regulatory Toxicology and Pharmacology 32, 228-247.

Cruzan, G., Cushman, Janette R., et al. (2001). Chronic toxicity/oncogenicity study of Styrene in CD-1 mice by inhalation exposure of 104 weeks. Journal of Applied Toxicology 21, 185-198.

IARC: The International Agency for Research on Cancer. (November, 1994). Some Industrial Chemicals : IARC Monographs on the Evaluation of Carcinogenic Risks to Humans 60, 233-320.

National Institute for Occupational Safety and Health. (January 2001). 9th Report on Carcinogens. U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program. Retrieved March 5, 2002, from http://ehis.niehs.nih.gov/roc/toc9.html

NTP chemical repository. Styrene [Electronic version]. U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program. Retrieved March 9, 2002 from http://ntpserver.niehs.nih.gov/htdocs/Chem_H%26S/NTP_Chem1/Radian100-42-5.html

Sherrington, EJ + Rees, HG. (April 2001). A community exposed to styrene during relining of a sewer in town in south Wales, UK. Journal of Toxicology: Clinical Toxicology 39(3), 230. Retrieved Feburary 25, 2002 from University of Minnesota Health Reference Center on-line database.