Combining Passive Sampling and Dosing to Unravel the Contribution of Hydrophobic Organic Contaminants to Sediment Ecotoxicity

Contaminated sediments are ubiquitous repositories of pollutants and cause substantial environmental risks. Results of sediment bioassays remain difficult to interpret, however, as observed effects may be caused by a variety of (un)known stressors. This study aimed therefore to isolate the effects of hydrophobic organic contaminants from other (non)chemical stressors present in contaminated sediments, by employing a newly developed passive sampling–passive dosing (PSPD) test. The results showed that equilibrium partitioning between pesticides or polyaromatic hydrocarbons (PAHs) in contaminated sediments and a silicone rubber (SR) passive sampler was achieved after 1–3 days. Chlorpyrifos concentrations in pore water of spiked sediment matched very well with concentrations released from the SR into an aqueous test medium, showing that SR can serve as a passive dosing device. Subjecting the 96 h PSPD laboratory bioassay with nonbiting midge (Chironomus riparius) larvae to field-collected sediments showed that at two locations, concentrations of the hydrophobic organic contaminant mixtures were high enough to affect the test organisms. In conclusion, the developed PSPD test was able to isolate the effects of hydrophobic organic contaminants and provides a promising simplified building block for a suite of PSPD tests that after further validation could be used to unravel the contribution of hydrophobic organic chemicals to sediment ecotoxicity.

The positive mode MS method used initially 70% of solvent A (MQ-water + 0.5% acetic acid) and 30% B (acetonitrile) at a flow rate of 0.3 mL/min.After the first 5 minutes at this eluent composition, which should elute inorganic impurities that go to the waste for the first 3 minutes, but still retain the most polar pesticides.Eluent B was increased stepwise up to 100% within 15 minutes, kept at 100% for 10 minutes and then switched back to 30% B for the final 4 minutes (29 minutes total run time).In between the samples, the HPLC equilibrated for 7 minutes at 30% B.
The results of the LC-MS/MS analysis were gathered with the Analyst Software.The analyte concentrations in the samples were calculated from these results by using pre-made calibration standards.For each analyte, an external calibration curve was constructed using

S5
Table S5.Compounds targeted in chemical profiling of the investigated sediments and their respective limits of quantification (LOQ) in positive mode.The fitted lines represent a first order exponential uptake curve.2020).With our applied settings, Here, we applied the threshold at maximum 20% depletion of OC-sorbed concentration, which would only be surpassed if 400 g or less sediment was used, for sediments with less than 2% OC, and at those limits it does not matter what the chemicals logK is (depending on the assumption of equal affinity for OC as for SR, which is well known to deviate to some extent).

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Assumptions: Equation 1 () = 10 mixed standards with known concentrations (333 -0.017 μg L-1), with signals detected for the most abundant specific fragments from parent compounds.Using a weighting factor of 1/(peak area 2 ) on the orders of magnitude range of the detection signal, a linear curve was then used to calculate the analyte concentrations in the sample.The calibration curves were plotted using least-square regression.Each analyte showed sufficient linearity for the LC-MS/MS analysis in the studied working range (Limit of quantification set as the lowest point of the calibration curve with accuracy 80-120%), with correlation coefficients (R2) greater than 0.950.Subsequently, the measured concentrations in each sample were converted into measured concentrations per sampler in Microsoft Excel by accounting for dilution steps and extraction volumes.

Figure S2 .
Figure S2.Survival of C. riparius larvae after 96 h of exposure to medium dosed by SR equilibrated (n = 5) with sediment originating from different locations (n = 25).Landuse: C = control, AS = artificial sediment, N = nature, A = agriculture, M = mixed, U = urban and W = WWTP.

Figure S3 .
Figure S3.Calculations and assumptions on passive dosing depletion

Figure
Figure S3 illustrates the influence of the OC content on the depletion of chemicals with different Koc, by the combinations 1g SR/800g sed (2g SR applied by us in 800 g sed) and 2g SR/400g sed, with a reference to the recommended equations in the Nature protocol on passive sampling by Jonker et al. (2020).With our applied settings, Here, we applied the threshold at maximum 20% depletion of OC-sorbed concentration, which would only be surpassed if 400 g or less sediment was used, for sediments with less than 2% OC, and at those limits it does not matter what the chemicals logK is (depending on the assumption of equal affinity for OC as for SR, which is well known to deviate to some extent).

10 6 ×Figure S4 .
Figure S4.Calculations and assumptions on passive sampling depletion.Note that both figures have identical data but Figure B applies a log scale Y axis to better display the chemical fractions predicted in food and larva.

Figure 4
Figure4illustrates the depletion of chemicals from the passive dosing material volume/test medium volume/and food content, for chemicals with a different partition coefficients ranging log 1-6.Here, we applied the threshold at maximum 20% depletion of SR concentration, which would also only be limited for chemicals with logK < 2.

Table S1 :
Table belonging to Figure 1 with additional information on the various components

Table S1 .
Overview of the investigated study sites of the passive sampling experiment.

Table S3 .
Overview of the seven pesticides used in the pesticide mixture sediment.

Table S4 .
Concentrations of pesticides in the pesticide mixture sediment.Chemical target analysis of sediment associated pesticides: QA/QC.

Table S6 .
Chemical target analysis of sediment associated PAH: QA/QC.Phenanthrene fluorescence was measured at 250/385 nm and pyrene fluorescence was measured at 335/383 nm.PAH concentrations were quantified with external standard calibrations at a minimum of 5 levels and an accuracy of the log-linear calibration curve within 5%.Measurements started with a 45:55 acetonitrile:water (v:v) solution.For PAH detection in the acetonitrile SR extracts, after 1 minute, the acetonitrile concentration was slowly increased to 80% at 8 minutes.From minute 8 to 11, the acetonitrile concentration was increased to 100%, after which the concentration was decreased to 45% at 15 minutes.Compounds targeted in chemical profiling of the investigated sediments and their respective limits of quantification (LOQ).
a lowest point on a log-linear 5 level calibration curve b using extraction of 0.1 g SR with 1.5 mL solvent, see Methods section in the manuscript c back-calculated from the log-linear calibration curve and the nominal concentration.S6Section S2.c back-calculated from the log-linear calibration curve and the nominal concentration

Table S7 .
Nominal concentrations for spiked sediments with chlorpyrifos.

Table S8 .
Overview of the investigated study sites.

Table S9 .
The equilibrium partitioning time for the uptake of organic compounds by silicon rubber from contaminated sediments a average K oc for 8 soils as reported in:De Jong, L. W., Moldrup, P., De Jong, H., Celis, R. (2008) Sorption and leaching of short-term-aged PAHs in eight European soils: link to physicochemical properties and leaching of dissolved organic carbon.Soil Science 173 (1), p 13-24, DOI: 10.1097/ss.0b013e31815aea32

Table S10 .
Results of the 96 h PSPD bioassays with first instar larvae (<24 h) of the non-biting midge C. riparius with chlorpyrifos spiked sediment.

Table S11a .
The measured freely dissolved concentrations predicted using equilibrium partitioning (EqP).Ratio EqP predictions versus dissolved concentration in PSPD via SPME.

Table S11b .
Silicone rubber concentration to polyacrylate partition coefficient.