Phthalates are ubiquitous in the modern environment, because they are not chemically bound to the plastic polymer and can readily leach out of the plastic. Some examples of materials that contain phthalates are food products, perfumes, hair sprays, nail polish, garden hoses, car interiors, lotions, and vinyl flooring. Food products are the most common products where humans are exposed to phthalates, because phthalates leach into the food from contact with plastics containing the chemical. Phthalates are poorly absorbed through the skin. After oral ingestion, phthalates are hydrolyzed from the diester to monoester form by lipases present in saliva, stomach and small intestine.
Lipases are also present in breast milk.
The monoester form is very rapidly absorbed by the gut. Upon absorption, the chemical is conjugated by the liver and excreted in the urine as a conjugated monoester phthalate. Evidence of oral phthalate exposure would therefore be indicated by the presence of the monoester in the serum or urine. However, if exposure to phthalate diesters is through intravenous tubing, then the diester form would be present in the serum. Based upon this information, it is likely that the serum levels of phthalate diesters reported in this study are assay contaminants and not the result of ingestion of the chemicals.