Tom Morrione, MD takes a closer look at the results of a poll question and examines the evidence of some of the toxins present in our environment.

by Tom Morrione, MD

Table 1. Poll Results

Question: Which toxin was most frequently found above accepted safety levels in the general U.S. population?   

Arsenic 

14 %

Lead 

5 %

Mercury 

24 %

Polycyclic Aromatic Hydrocarbons (PAHs) 

0 %

Polychlorinated Biphyenyls (PCBs) 

33 %

Tobacco Smoke 

24 %

Hopefully, many of you were troubled by the phrase “accepted safety levels” in the question.  This has an ominous overtone much like the concept of collateral damage in that there exists an acceptable level of exposure that will not cause any noticeable or measurable deleterious affect.  It may be that technology and the lowest detectable level determine safety.

The general population is exposed to an alarming number of toxins on a daily basis.  Some may argue (justifiably) that any exposure has a significant affect on the health of an individual, but through scientific analysis, observation and general consensus, thresholds have been established defining accepted safety levels for some toxins, not all.  Over the course of time, and with more studies and information, it is not uncommon to see these thresholds change and often be reduced.  For example, it was only in 2001 that the acceptable level of arsenic in water was reduced 80% from 50ppb to 10ppb.  For other toxins, a detectable presence may be considered toxic.  

Arsenic

As an odorless and tasteless semimetal, arsenic toxicity is mostly present with water contamination.  Rural well water is a common culprit with cases in the U.S.  The current acceptable safety limit is 10ppb dropped from 50ppb in 2001, with the intent to reduce the development of toxicity and associated morbidity and mortality related to bladder and lung cancers.  However, the supporting evidence is largely based on a demonstrated relationship between arsenic exposure and cancer in the Blackfoot-disease (BFD) area of Taiwan.  At all curious if your area is questionable for elevated groundwater levels?  The U.S. Geological Survey constructed a map based on samples from counties throughout the U.S. with corresponding color-coded concentrations (http://water.usgs.gov/nawqa/trace/pubs/geo_v46n11/fig2.html).  For example, most of Maine is lit up with 5ppb, with a large central portion showing 10ppb.  One public health study conducted in 2004 showed an increased presentation of depression and cardiovascular problems in those with levels greater than 2ppb.  Unfortunately, while I was able to easily find data correlating increased health risks with acute and chronic arsenic exposure, data on incidence or prevalence of arsenic poisoning in the U.S. was not readily available. 

Lead

Lead toxicity is well known and studied in the U.S.  We no longer have leaded gasoline, but it is readily found in older paint in houses, plumbing, solder and ceramic glazes.   Since unleaded gasoline and removing the lead from the solder from canned goods, the lead exposure to the general population lies mostly with children and degrading lead paint and subsequent surrounding environmental contamination.  In 1991, the Center for Disease Control (CDC) established a cutoff for safe lead levels at 10mg/dL in children.  This is becoming increasingly challenged as recent studies suggest neurocognitive and developmental deficits with blood levels < 10mg/dL.  National Health and Nutrition Examination Survey (NHANES) subsamples revealed the following exposure levels:

Table 2.  NHANES Data for Blood Lead Levels

2001-2002 Data

mg/L (Geometric Mean with 95% CI)

Total, age 1 and >

1.45

Age Group

 

  1-5 years

1.70

  6-11 years

1.25

  12-19 years

.942

Gender

 

  Males

1.78

  Females

1.19

Race/Ethnicity

 

  Mexican Americans

1.46

  Non-Hispanic Whites

1.43

  Non-Hispanic Blacks

1.65


In 2001, 3.09% of the 2.4 million children tested had blood levels > 10mg/dL.  While high and a clear target for improvement, this is a vast reduction from previous figures of 87.4% of children with levels > 10mg/dL during in our recent past when gas was leaded.

Mercury

Mercury toxicity may result from exposure from multiple sources.  It is widely used in electrical equipment, batteries, pigments, dental amalgam, pharmaceutical preservatives and cosmetics.  Perhaps the largest source is from eating contaminated seafood.  Blood levels are measured in mg/L and toxicity becomes evident clinically with levels > 100 mg/L.  The American Conference of Industrial Hygienists (ACGIH) recommends an upper limit of 15 mg/L.  NHANES data reveals the following exposure levels in the general population:

Table 3: NHANES Data for Mercury Levels

Age

mg/L (Geometric Mean with 95% CI)

  1-5 years

.318

    Males

.329

    Females

.307

  16-49 years (female only)

1.02

Race/Ethnicity

 

  Mexican Americans

.667

  Non-Hispanic Whites

.800

  Non-Hispanic Blacks

1.06


All the values are well below the accepted safety levels mentioned above for individual toxicity levels.  Women of childbearing ages 16 to 49 are of particular interest as studies have shown that levels as low as 58 mg/L are associated with developmental delays.  Remember that the data above reflects a CI of 95% and that means that 5% still fall outside the group, both in the high and low range.  In fact, the same data demonstrated that about 5% of women 16-49 had levels from 5.8 to 58 mg/L.  The EPA has determined, based on outcome studies, a safe ingestion amount for the general population of 0.1mg/kg/day, but there is no specific serum concentration that corresponds to the weight calculation as of yet. 

Polycyclic aromatic hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons (PAHs) are released with the partial combustion of organic products such as fossil fuels, tobacco and grilled meat.  Exposure occurs through various mediums including soil, water, food and air.  This happens as a result of our vehicle exhausts, furnace and chimney smoke, as well as that tasty overcooked charbroiled hamburger.  NHANES analyzed levels of 9 common PAHs via 22 separate metabolites in a subsample, with age > 6 representative of the general population.  Of these, pyrene is a common component of PAH and frequently a measure for exposure.  The NHANES data showed an increased concentration in ages 6-11 and other studies confirmed higher exposure for urban residents than their rural counterparts. Otherwise, there appeared no statistical significance between age, ethnicity or gender.  Another known component of PAHs is naphthalene, also tested in the NHANES data.  Results indicated higher concentrations in females, Mexican Americans and ages 20 and older.  Results, however, were not present for many of the PAHs and metabolites with less than detectable limits.

Polychlorinated biphenyls (PCBs)

Polychlorinated biphenyls (PCBs) include a group of manufactured organic chemicals of 209 individual chlorinated chemicals and, in concentrated form, PCBs are either oily liquids or solids without smell or taste.  PCBs were widely used as insulation in electronic equipment and as a coolant and lubricant.  Disposal difficulties and developing health concerns resulted in PCBs no longer being produced after 1977 and, ultimately, were banned in the U.S. in 1979.  Because of their resilience to degradation, the toxin is still prevalent in the environment and has a tendency to increase in concentration moving up the food chain. Most exposure occurs eating contaminated fish.  Five of 12 tested congeners in the NHANES data had statistically significant levels detected (ages 20 and older).  Of these five tested , two are responsible for 80-90% of the toxin exposure.  One of the two had values of mid 30s (pg/g) in all groups, with the exception of Mexican Americans, who tested at 50% of counterparts.  The other showed a similar distribution, with values of low 20s (pg/g) with a 22% reduction in Mexican Americans. 

Tobacco

The largest source of exposure to tobacco is through cigarettes, which contain approximately 1.5% of nicotine by weight.  Somewhat surprising when you consider the remaining 98.5% contains a large number of other toxins not covered here.  It can be absorbed via the gastrointestinal tract via nicotine gums or chewing tobacco, through the skin with nicotine patches, or through direct contact with the harvested leaves.  Ninety-two percent of nicotine is absorbed into the blood stream through the lungs with inhalation with a half-life of several hours, and levels can be tested by checking cotinine in the serum, saliva, hair and urine.  Active smokers have levels > 10ng/mL and often in the 100s.  Nonsmokers exposed to low levels of environmental tobacco usually have levels < 1ng/mL. 

Serum cotinine levels were measured in a NHANES subsample.  Using only nonsmokers (defined as a cotinine level < 10ng/mL), the group was broken down into age, gender and race/ethnicity.  The most recent data from NHANES 1999-2001 showed the following:

Table 4: NHANES Data for Cotinine Levels

Age

Ng/mL (Geometric Mean with 95% CI)

  3-11 years

.110

  12-20 years

.086

  > 20 years

.052

Gender

 

  Male

.075

  Female

.053

Ethnicity

 

  Mexican Americans

.060

  Non-Hispanic Whites

.052

  Non-Hispanic Blacks

.164


Unlike arsenic and mercury, there appears to be no acceptable safety exposure to tobacco and the data above will help to guide policy over time and to evaluate trends.  In fact, when compared with NHANES data from 1988-1991, there is a reduction of 68% in children, 69% in adolescents and 75% in adults. This data is strongly suggestive of a significant decrease in exposure in the general population.

Summary

Referring back to the original question, the majority of responses felt the most frequently found toxin above safety levels in the U.S. was PCBs, followed by a tie between mercury and tobacco.  One could argue that tobacco and exposure to PAHs go hand-in-hand, though no one correctly chose it as the frequently found toxin.  The data is much like comparing apples and dump trucks, and it appears that the great majority of the population is exposed to the toxins, but at a level that is less than toxic.  Is there a safe level of exposure to tobacco, lead, mercury, PAHs or PBCs?  Hopefully, there is since likely each one us is exposed to one, if not more, of the above on a daily basis.  Just think about your trip to work…

Tom Morrione, MD
Family and Geriatric Medicine
Maine Medical Center Partners

References:

http://www.cdc.gov/nchs/nhanes.htm [Accessed November 2008]

http://dhs.wisconsin.gov/eh/hlthhaz/fs/PCBlink.HTM#What%20are%20PCBs? [Accessed November 2008] 

http://www.epa.gov/safewater/arsenic/basicinformation.html [Accessed November 2008]

http://www.groundwater.org/au/archives/aq_1604.pdf [Accessed November 2008]

Zierold, K et el. Prevalence of Chronic Diseases in Adults Exposed to Arsenic-Contaminated Drinking Water. American Journal of Public Health. November 2004, Vol 94, No. 11: 1936-1937