Phthalates in drinking water affect thyroid hormone, finds lab study.

Oct 18, 2010

Li, N, D Wang, Y Zhou, M Ma, J Li and Z Wang. 2010. Dibutyl phthalate contributes to the thyroid receptor antagonistic activity in drinking water processes. Environmental Science and Technology http://dx.doi.org/10.1021/es101254c.

Synopsis by Heather Stapleton

Treated drinking water contains phthalate chemicals that interfere with thyroid hormone actions, raising concerns about exposure to these ubiquitous pollutants.

Contaminants found in both treated and untreated drinking water can interfere with the basic action of thyroid hormones, which regulate many essential body processes, finds a study from China. The biggest culprits were two types of chemical additives called phthalates – DBP and DEHP.

This is the first study to report that both untreated and treated drinking water contain chemicals that can decrease thyroid hormone receptor actions. The findings raise concerns about chemicals widespread in drinking water that could impact thyroid regulation, and possibly alter metabolism and development in the body that the hormones control.

Numerous studies have investigated levels of pharmaceutical compounds and measured chemicals that alter hormone actions – endocrine disrupting chemicals – in drinking water. Some of them – such as phthalates – can also affect the thyroid hormone system. Thyroid hormones are necessary for a wide variety of responses in people, including growth, metabolism and brain development in children. They also play a role in fertility and regulate reproduction in adults.

Phthalates are widely used in plastics, polyvinyl chloride, personal care products and many other items. Diethylhexyl phthalate (DEHP) and dibutyl phthalate (DBP) are two common types. DEHP helps keep hard materials flexible and soft and is added to a variety of products, including medical tubing and shower curtains. Personal care products, such as perfumes, lotions and shampoos, often contain DBP as solvents that extend the lifespan of the fragrances.

Prior lab and animal studies show that both can interfere with thyroid hormone actions. The chemicals can cross the placenta and are known to alter development and reproduction in animals. Human exposure is high because of their common and widespread use. Phthalates have been measured in people and the environment, including drinking water. Due to concerns about their toxicity, both the European Union and the United States have restricted the use of some phthalates (including DBP and DEHP) in children's toys.

Researchers in China used a yeast assay to determine if chemicals in pretreated and treated drinking water could affect the way thyroid hormones regulate cell processes. They collected pretreated water from a reservoir in Beijing and water that was treated by chlorination, coagulation and filtration.

In the lab, they determined if the water affected the way a thyroid hormone (triiodothyronine) attached to a thyroid receptor – the first step in regulating cell processes that affect growth, metabolism and development. The water was analyzed for chemicals – organochlorine pesticides, phenols and phthalates – that may contribute to the effect.

None of the six water samples tested increased the ability of the thyroid hormone to interact with the receptors.

However, all six water samples – regardless of whether or not they were treated – significantly inhibited the hormone from attaching to the thyroid receptor. DBP accounted for most of this inhibition of thyroid activity, while DEHP made a small contribution.

Levels of DBP did not change significantly from drinking water treatment, and thus the concentrations of DBP were the same in the reservoir as compared to what people receive in their homes. However, the levels were most likely higher than reports for the same chemicals in other parts of the world.

The authors recommend better integrated management practices and drinking water treatments to prevent thyroid-altering chemicals from contaminating drinking water supplies.