Examining the relevance of the microplastic-associated additive fraction in environmental compartments SUPPORTING INFORMATION

Table S1. Examples of relevant additives for the modelling undertaken in the present study, together with their CAS number, logKow or logP, their function and application, typical concentrations in plastic products and examples of concentrations reported for matrices such as sediment and sewage sludge or effluents. Figure S1. Simulated variation in the proportion of model plastic-incorporated chemical additive (CAD) in a sample (NP-CAD/NS-CAD) as a function of the organic carbon (OC) content to plastic x ratio of

Table S1.Examples of relevant additives for the modelling undertaken in the present study, together with their CAS number, logK ow or logP, their function and application, typical concentrations in plastic products and examples of concentrations reported for matrices such as sediment and sewage sludge or effluents.

Figure S1
. Simulated variation in the proportion of model plastic-incorporated chemical additive (CAD) in a sample (N P-CAD /N S-CAD ) as a function of the organic carbon (OC) content to plastic x ratio of the sample and the K pw and K oc of the chemical additive.For this simulation, the C CAD-free was set to 1 ng L -1 , f Px to 0.2, P Px to 0.001 and the proportion of CAD in the plastic x = 5 %.

Figure S2.
Simulated distribution of a model chemical additive (CAD) between presence as a plastic additive, sorbed to plastic, and sorbed to organic carbon (OC) as a function of the OC content to plastic x ratio of the sample and the proportion of additive-loaded plastic f Px .For this simulation, the C CAD-free was set to 1 ng L -1 , logK pw K oc = 5, P Px = 0.001, P = 0.08, and the proportion of CAD in the plastic x = 5 %.

Figure S3
. Simulated concentration ratios of a model chemical additive (CAD) over that of a reference chemical for (i) freely dissolved concentrations (C Free ) and concentrations for sorbed to particulate (C Part ) organic carbon (OC) and plastic with and without the presence of the CAD as an additive in a proportion f Px of additive-loaded plastic.For this simulation, the C CAD-free was set to 0.03 ng L -1 , logK pw and K oc = 6, P = 0.01, and the proportion of CAD in the plastic x = 5 %.The C Free was set to 0.1 ng L -1 for the reference chemical, and logK pw and K oc = 5.

Figure S4
. Simulation of the proportion of a model chemical additive dissipating from microplastic particles with a diameter of 1, 0.1, 0.01, 0.001, 0.0001, and 0.0001 mm over periods of 0.5 and 10 days, 1 and 10 years.These simulations assume that transport in the polymer is the main resistance to mass transfer of the chemical from the particle to the outer environment.

Examples of relevant additives
Table S1 presents a range of example additives relevant to the modelling undertaken in this study.This list is not exhaustive but mostly includes substances identified through ECHA's plastic additive mapping exercise.A few of these substances have high pKa but are not expected to be dissociated at pH of 6-8.Substances included are mostly flame retardants, plasticisers and UV stabilisers.More comprehensive lists of relevant chemicals can be found elsewhere [1][2][3][4][5][6] .
Table S1.Examples of relevant additives for the modelling undertaken in the present study, together with their CAS number, logK ow or logP, their function and application, typical concentrations in plastic products and examples of concentrations reported for matrices such as sediment and sewage sludge or effluents.Simulated distribution of a model chemical additive (CAD) between presence as a plastic additive, sorbed to plastic, and sorbed to organic carbon (OC) as a function of the OC content to plastic x ratio of the sample and the proportion of additive-loaded plastic f Px .For this simulation, the C CAD-free was set to 1 ng L -1 , logK pw K oc = 5, P Px = 0.001, P = 0.08, and the proportion of CAD in the plastic x = 5%. .Simulated concentration ratios of a model chemical additive (CAD) over that of a reference chemical for (i) freely dissolved concentrations (C Free ) and concentrations for sorbed to particulate (C Part ) organic carbon (OC) and plastic with and without the presence of the CAD as an additive in a proportion f Px of additive-loaded plastic.For this simulation, the C CAD-free was set to 0.03 ng L -1 , logK pw and K oc = 6, P = 0.01, and the proportion of CAD in the plastic x = 5 %.The C Free was set to 0.1 ng L -1 for the reference chemical, and logK pw and K oc = 5.

Figure S4
. Simulation of the proportion of a model chemical additive dissipating from microplastic particles with a diameter of 1, 0.1, 0.01, 0.001, 0.0001, and 0.0001 mm over periods of 0.5 and 10 days, 1 and 10 years.These simulations assume that transport in the polymer is the main resistance to mass transfer of the chemical from the particle to the outer environment.

4 Figure S1 .
Figure S1.Simulated variation in the proportion of model plastic-incorporated chemical additive (CAD) in a sample (N P-CAD /N S-CAD ) as a function of the organic carbon (OC) content to plastic x ratio of the sample and the K pw and K oc of the chemical additive.For this simulation, the C CAD-free was set to 1 ng L -1 , f Px to 0.2, P Px to 0.001 and the proportion of CAD in the plastic x = 5%.

m
Figure S3.Simulated concentration ratios of a model chemical additive (CAD) over that of a reference chemical for (i) freely dissolved concentrations (C Free ) and concentrations for sorbed to particulate (C Part ) organic carbon (OC) and plastic with and without the presence of the CAD as an additive in a proportion f Px of additive-loaded plastic.For this simulation, the C CAD-free was set to 0.03 ng L -1 , logK pw and K oc = 6, P = 0.01, and the proportion of CAD in the plastic x = 5 %.The C Free was set to 0.1 ng L -1 for the reference chemical, and logK pw and K oc = 5.

Table S2 .
Examples of reported diffusion coefficients of additives in plastics or plastic particles.