Allergies more likely in Bulgarian children exposed to pththalates in dust.

What did they do?

In mid-2004, questionnaires on housing and health were sent to all the parents of young children (ages 2, 3, 5 and 7 years old) in selected districts of two Bulgarian cities. The parents of 4,479 children returned the survey (a response rate of 35 percent).

Of those, 730 potential cases and 1,275 potential controls were identified. Cases were the children who were reported to have at least 2 of these 3 symptoms: wheezing during the last 12 months, rhinitis during the last 12 months when not having a cold or itching rash eczema in the last 12 months. Potential controls reported none of these three symptoms or several other allergy and asthma questions.

Follow up questionnaires, late refusals by parents and technical errors gave final numbers of 102 cases and 82 controls.

Inspectors visited the homes of the 184 children and collected dust samples from above floor level (e.g., over the door) in each child's room, as was done in the DBH study. Six phthalates were measured in these dust samples, and expressed as a fraction of the total weight of the collected dust.

Researchers then calculated the likelihood that children were cases, rather than controls, as a function of the percent phthalate in the house dust samples. Adjustments were made for the child's age and gender, smoking in the home (current; or during pregnancy/first year of life) and the presence of allergy or asthma symptoms in any other family member.

What did they find?

Of the six phthalates measured, DEHP level in the dust was associated with both case status and wheezing in the last 12 months. Specifically, children in homes with the highest levels of DEHP, when compared with children having the lowest levels, were 2.9 times more likely to be a case rather than a control, and 3.7 times more likely to report wheezing in the last 12 months.

No other phthalates were significantly associated with wheezing, rhinitis, eczema or case status in this study.

In Bulgaria, the common word for linoleum and PVC-based flooring is the same – "balatum". Since neither the survey nor the inspectors could reliably distinguish between these two types of balatum, it was not possible to specifically examine the relationship between PVC-flooring in a child's room and presence of symptoms. However, the presence of any type of balatum (as reported by inspectors) increased the odds of case status by 2.2 times, wheezing during the last 12 months by 2.6 times and rhinitis by 2.2 times. No association was found between phthalates in the dust and balatum flooring.

The use of polishing products when dusting was significantly associated with increased (1.9 times greater) odds of wheezing in the last 12 months and with the levels of butyl benyl phthalate (BBzP) and di-n-octyl phthalate (DnOP) in the indoor dust. More frequent cleaning was associated with fewer health problems and with lower levels of BBzP in the dust.

Only 35 percent of households responded to the original questionnaire. Low response rates can skew results if the non-responders are different from those who respond. To assess whether biased non-response happened in this study, the researchers surveyed by phone 240 randomly selected households that failed to return the original questionnaire.

Excluding the eczema and family members with allergy/asthma questions, no statistically significant differences between the two groups were found. The prevalence of wheezing, rhinitis and eczema was greater in the subjects that agreed to home inspections as compared with those who only answered the survey. Since exposures were determined by laboratory testing rather than survey questions, this higher prevalence is unlikely to have biased the study's results.

What does it mean?

In this study, DEHP levels in the dust of children's rooms were associated with increased risk of asthma and allergy symptoms.

These results are similar to those found in the earlier Swedish study and add to the likelihood that the results represent real DEHP health effects rather than chance or confounded findings. Although the Swedish study found an association between BBzP in dust and rhinitis and eczema, this study did not, which reduces the likelihood that the earlier BBzP findings represent true effects.

If DEHP is indeed aggravating asthma, as suggested by this study, it could be acting as an adjuvant and increasing allergic responses to allergens already in the environment. A 2006 study from Japan found that DEHP can act as an adjuvant, as it increased the effects of dust mite allergen in mice. However, research results on this question are inconsistent and the question is far from settled.

Neither the Bulgarian study nor the earlier Swedish study incorporate time into the design such that the diseases are measured months or years after the exposures. This lack of time sequencing makes "reverse causation" a risk – the possibility that the disease may be causing the (innocent) exposure, instead of the exposure causing the disease.

If this study were done in the United States, it would be particularly vulnerable to this problem, since people with allergies might exchange wall-to-wall carpeting (common in the U.S.) for less-dusty PVC-based flooring, thus creating a false linkage between PVC and allergy. But wall-to-wall carpeting is rare in Sweden, and so the argument makes little sense there. Whether it makes sense in Bulgaria is not described by the authors.

In summary, this study shows an association between the level of DEHP (the common phthalate plasticizer) in dust and asthma/allergy symptoms in Bulgarian children. This result is similar to that found by an earlier study conducted in Sweden and strengthens the possibility that DEHP exposure is actually causing or aggravating disease.

Cohort studies - a type of case-control study that incorporates time between exposure and onset of disease - with similar findings would strengthen these results. The authors are now conducting a birth cohort study that will further test these findings and determine the importance of early life exposures to endocrine disrupting chemicals on the development of asthma, allergies and other disease.