Predicting plant uptake of pharmaceuticals
from soils is very challenging
because many pharmaceuticals are ionizable compounds, which experience
highly variable sorption/desorption and transformation processes in
soils. This study aimed to elucidate how the equilibrium between sorbed
and dissolved phases influences radish uptake of 15 pharmaceuticals
from three soils with different properties. After 30 days of uptake,
the accumulation of acetaminophen, carbamazepine, lamotrigine, carbadox,
trimethoprim, and triclosan in radish ranked as Riddles > Capac
>
Spinks soil. In contrast, radish accumulation of caffeine, lincomycin,
monensin, tylosin, sulfadiazine, and sulfamethoxazole exhibited the
opposite order of Riddles < Capac < Spinks soil. Oxytetracycline
and estrone demonstrated similar accumulation in radish grown in the
three soils. Accumulation of pharmaceuticals in radish demonstrated
no apparent relation with their concentration in soils. However, we
identified strong positive correlation between pharmaceutical accumulation
in radish and their corresponding concentration in soil pore water.
These results reveal that pharmaceutical in soil pore water is the
dominant fraction bioavailable to plant uptake. Relatively constant
root concentration factors (RCFs) on the basis of pharmaceutical concentration
in soil pore water, compared to the highly variable RCFs derived from
soils, suggest that pore water-based RCF is superior for describing
pharmaceutical accumulation in plants grown in soils. We recommend
that pharmaceuticals in soil pore water should be evaluated and included
in modeling their uptake by plants.