When the Exposure Matrix Is Also the Target Organ: Interpreting Urinary Phthalate Biomarkers in Pregnancy

Phthalate exposure during pregnancy may affect placental and renal biology, but the biological interpretation of urinary exposure and effect biomarkers remains challenging. McNell et al. provide an important longitudinal framework by relating early-pregnancy urinary phthalate metabolites to urinary biomarkers related to placental angiogenesis and renal biology measured across gestation. Their study also highlights two interpretive issues. First, an exposure biomarker obtained in early pregnancy and a biological-response trajectory extending into late pregnancy represent different temporal processes. Second, urine serves simultaneously as the matrix for exposure assessment and for assessment of renal biological responses, while the kidney itself may be a toxicological target. Thus, urinary phthalate-protein associations should not automatically be interpreted as direct evidence of organ toxicity. Future studies integrating repeated exposure measurements, complementary biological matrices, direct functional measures, and longitudinal trajectory analyses may provide a more mechanistic framework for understanding reproductive toxicity.