Measuring exposure to phthalates not a simple task.

Preau Jr., JL, L-Y Wong, MJ Silva, LL Needham and AM Calafat. 2010. Variability over one week in the urinary concentration of metabolites of diethyl phthalate and di(2-ethylhexyl) phthalate among 8 adults: an observational study. Environmental Health Perspectives http://dx.doi.org/10.1289/ehp.1002231.

To better understand the levels of phthalates that people are routinely exposed to, researchers may need to be more careful about the way they measure the environmental chemicals. 

In a typical research study, scientists look at exposure to many different phthalates at the same time. They also tend to assess human exposure by measuring the chemicals in a single urine sample taken either as a one-time collection (or “single-spot”), a collection first thing in the morning or a combined collection over a full 24-hour period. Because phthalates pass through the body in a matter of hours, the single samples may mislead because they do not reflect differences in daily, day-to-day and type of phthalate exposure levels. 

Therefore, customizing sampling and measurement methods – depending on the question and the type of phthalate at hand – may result in a more reliable estimate of phthalate exposure, explain the authors of the research paper.

These findings are important in that they can help scientists plan future research that will more accurately quantify phthalate exposures through various sources. They are also helpful for evaluating the results of previous studies.

Phthalates are a group of related chemicals found in varying levels in a wide range of applications and consumer products, including building materials, plastics and beauty products. Certain phthalates make plastics – such as polyvinyl chloride – soft for use as toys, in medical tubing/bags and shower curtains. Different types are found in adhesives, wood finishes and cosmetics.

While some phthalates (such as DEHP) are particularly common in food, others (like DEP) are found primarily in personal care products. Distinguishing among them can be important, as phthalates may differ in their ability to derail normal development and hormonal activity. For instance, DEHP is believed to be particularly disruptive to the development of the male reproductive system, whereas DEP has not shown such effects.

In this study, researchers followed eight adults for a week, collecting roughly eight urine samples per subject each day. They measured phthalate levels and looked at how much those levels varied across time. Levels of the phthalates primarily found in beauty products tended to vary widely, probably because of vastly different personal care routines and habits. Great differences in an individual’s levels were seen across the course of a day, since the products tend to be applied at the same time each day – for instance, in the morning, rather than in the evening. From day to day, a subject’s levels were fairly constant. When assessing these types of phthalates, a single sample at a specific time might be best.

By contrast, for phthalates found mostly in food, levels were quite different throughout the day and from day to day, even within the same person. This most likely reflects variations in diet. This implies that in order to capture phthalate exposure through food, urine samples taken at several times during the day and over several days are recommended. Single-spot samples are likely to be insufficient.