A majority of persistent organic
pollutants (POPs) that we see
today have in fact undergone extensive aging in the environment, as
their use was discontinued several decades ago. While contaminant
aging is commonly believed to lead to reduced bioavailability, at
present there is not a direct method for quantitatively determining
the effect of aging. Here we propose a method based on the addition
of isotope-labeled reference compounds to field-collected soil or
sediment and comparison of the bioavailability between aged POPs and
their freshly added isotope-labeled counterparts. We demonstrated
this method using bioaccumulation by invertebrates and 24 h Tenax
desorption as bioavailability end points. Compared to the freshly
added isotope-labeled references, biota-to-soil/sediment accumulation
factors (BSAFs) of native (aged) DDTs (p,p′-DDD, p,p′-DDE,
and p,p′-DDT) and PCBs (PCB52
and PCB70) were consistently smaller, indicating that aging decreased
their bioaccumulation potential. For two aged soil samples from Florida,
BSAFs for earthworm (Eisenia fetida) decreased by
29.3–62.8% for DDT derivatives and 18.3–34.4% for the
PCBs. In aged marine and lake sediments from California, BSAFs for
indicator invertebrates (Nereis virens and Lumbriculus variegatus) decreased by 19.4–67.5% for
DDTs and 12.0–46.9% for the two PCBs. Similar reductions were
also observed when the same samples were analyzed using 24 h Tenax
desorption. Given that mass spectrometry is widely available, a simple
method based on the addition of isotope-labeled analogues may be easily
adopted and will be of great value for quantifying aging effects to
refine risk estimates of contaminated soil and sediment sites, including
the need for remediation intervention.