14 research outputs found
Modeling Uptake of Selected Pharmaceuticals and Personal Care Products into Food Crops from Biosolids-Amended Soil
Biosolids
contain
a variety of pharmaceuticals and personal care
products (PPCPs). Studies have observed the uptake of PPCPs into plants
grown in biosolids-amended soils. This study examined the ability
of Dynamic Plant Uptake (DPU) model and Biosolids-amended Soil Level
IV (BASL4) model to predict the concentration of eight PPCPs in the
tissue of plants grown in biosolids-amended soil under a number of
exposure scenarios. Concentrations in edible tissue predicted by the
models were compared to concentrations reported in the literature
by calculating estimated human daily intake values for both sets of
data and comparing them to an acceptable daily intake value. The equilibrium
partitioning (EqP) portion of BASL4 overpredicted the concentrations
of triclosan, triclocarban, and miconazole in root and shoot tissue
by two to three orders of magnitude, while the dynamic carrot root
(DCR) portion overpredicted by a single order of magnitude. DPU predicted
concentrations of triclosan, triclocarban, miconazole, carbamazepine,
and diphenhydramine in plant tissues that were within an order of
magnitude of concentrations reported in the literature. The study
also found that more empirical data are needed on the uptake of cimetidine,
fluoxetine, and gemfibrozil, and other ionizable PPCPs, to confirm
the utility of both models. All hazard quotient values calculated
from literature data were below 1, with 95.7% of hazard quotient values
being below 0.1, indicating that consumption of the chosen PPCPs in
plant tissue poses de minimus risk to human health
Dynamic Passive Dosing for Studying the Biotransformation of Hydrophobic Organic Chemicals: Microbial Degradation as an Example
Biotransformation plays a key role in hydrophobic organic
compound
(HOC) fate, and understanding kinetics as a function of (bio)Āavailability
is critical for elucidating persistence, accumulation, and toxicity.
Biotransformation mainly occurs in an aqueous environment, posing
technical challenges for producing kinetic data because of low HOC
solubilities and sorptive losses. To overcome these, a new experimental
approach based on passive dosing is presented. This avoids using cosolvent
for introducing the HOC substrate, buffers substrate depletion so
biotransformation is measured within a narrow and defined dissolved
concentration range, and enables high compound turnover even at low
concentrations to simplify end point measurement. As a case study,
the biodegradation kinetics of two model HOCs by the bacterium Sphingomonas paucimobilis EPA505 were measured at
defined dissolved concentrations ranging over 4 orders of magnitude,
from 0.017 to 658 Ī¼g L<sup>ā1</sup> for phenanthrene
and from 0.006 to 90.0 Ī¼g L<sup>ā1</sup> for fluoranthene.
Both compounds had similar mineralization fluxes, and these increased
by 2 orders of magnitude with increasing dissolved concentrations.
First-order mineralization rate constants were also similar for both
PAHs, but decreased by around 2 orders of magnitude with increasing
dissolved concentrations. Dynamic passive dosing is a useful
tool for measuring biotransformation kinetics at realistically low
and defined dissolved HOC concentrations
Experimental Results and Integrated Modeling of Bacterial Growth on an Insoluble Hydrophobic Substrate (Phenanthrene)
Metabolism of a low-solubility
substrate is limited by dissolution
and availability and can hardly be determined. We developed a numerical
model for simultaneously calculating dissolution kinetics of such
substrates and their metabolism and microbial growth (Monod kinetics
with decay) and tested it with three aerobic phenanthrene (PHE) degraders: <i>Novosphingobium pentaromativorans</i> US6-1, <i>Sphingomonas</i> sp. EPA505, and <i>Sphingobium yanoikuyae</i> B1. PHE
was present as microcrystals, providing non-limiting conditions for
growth. Total PHE and protein concentration were tracked over 6ā12
days. The model was fitted to the test results for the rates of dissolution,
metabolism, and growth. The strains showed similar efficiency, with <i>v</i><sub>max</sub> values of 12ā18 g dw g<sup>ā1</sup> d<sup>ā1</sup>, yields of 0.21 g g<sup>ā1</sup>, maximum
growth rates of 2.5ā3.8 d<sup>ā1</sup>, and decay rates
of 0.04ā0.05 d<sup>ā1</sup>. Sensitivity analysis with
the model shows that (i) retention in crystals or NAPLs or by sequestration
competes with biodegradation, (ii) bacterial growth conditions (dissolution
flux and resulting chemical activity of substrate) are more relevant
for the final state of the system than the initial biomass, and (iii)
the desorption flux regulates the turnover in the presence of solid-state,
sequestered (aged), or NAPL substrate sources
Estimated soil-water partition coefficient <i>K<sub>d</sub></i> (SauvƩ regression) vs. measured <i>K<sub>d</sub></i> (determined from CaCl<sub>2</sub> extractions).
<p>The dotted line indicates a ratio of one.</p
Measured soil parameters (depth, dry density <i>Ļ<sub>S,dry</sub></i>, field capacity, <i>FC,</i> and permanent wilting point, <i>PWP</i>) of the soil layers.
<p>Measured soil parameters (depth, dry density <i>Ļ<sub>S,dry</sub></i>, field capacity, <i>FC,</i> and permanent wilting point, <i>PWP</i>) of the soil layers.</p
Leaching of water from soil layer 2.
<p>Model compared to measurement for CTR, MSW and GSW treatments. Model is average of all predictions, min and max is minimum and maximum lysimeter measurements, MSW(I) and CTR(II), respectively.</p
Amendment application (second half of September in each given year) and input of Cd and Pb with amendment for the different treatments.
<p>GWS: Co-compost of green waste and sewage sludge, BIOW: Biowaste compost, FYM: Farmyard manure and MSW: Municipal solid waste compost.</p
Overview of the field and simulation study.
<p>For wheat and barley the starting point of growth takes place after seeding.</p
Simulated water balance and content of soil.
<p>(a) Simulated annual water balance, control scenario, August 1998 to October 1999; (b) simulated water content of the five soil layers, same simulation event.</p
Comparison of predicted and measured concentrations in plants (mg kg dw<sup>ā1</sup>) for the five treatments.
<p>October 1999 to July 2007. Model predictions are connected by lines for clearer comparison to measured values. Vertical lines denote the range of measured values and symbols the medians of the four replicates (values below QL were set equal to Ā½ QL (note that QLs from 1999ā2005 were applied for all years). Top arrows recall the time of amendment application.</p