An issue about the solid–water partition coefficient (Kd) in ChemicalDrift?

[lihu8918]

I was using the ChemicalDrift to simulate the transport and transform of an micropollutant, I have some questions about the solid–water partition coefficient (Kd):

1. what's the unit of Kd in the model, I noticed that the unit of Kd in the published paper (Aghito et al., 2023) is L/Kg, while the listed unit by the o.list_configspec() is m3/Kg. So which one is correct?
2. How to give Kd in the ChemicalDrift model? I noticed that Kd can be given directively, but many params that are relative to caculating Kd can also be given the model (eg., LogKOW, KOC_sed, fOC_sed). So the model use the given Kd directively, or caculate Kd by the relative params (eg., LogKOW, KOC_sed, fOC_sed)?

[knutfrode]

@manuelaghito can probably comment on this

[manuelaghito]

1. in the code of ChemicalDrift Kd are expressed in m3/Kg
2. for metals Kd is given directly. For organic compounds the Kd is calculated internally by multiplying KOC with fOC. You can choose to set KOC directly if you have data, but often it is easier to set KOW (expressed by Log KOW). Then there are empirical relationships used to estimate KOC from KOW, described in the paper.

(by the way... both in the paper and in the code we indicate KOW in L/Kg. This is wrong, KOW is unitless because is the ration of two concentrations in liquid fases, concentration in octanol over concentration in water, (g/L)/(g/L), so it is unitless.)

[manuelaghito]

keep in mind that the empirical relationships for converting KOW to KOC were obtained for PAHs... I am not sure how well these would apply to other organic chemicals. But if you have data for KOC you don't need these.

[lihu8918]

@manuelaghito thank you very much for your rely!
That is to say, For organic compounds, the Kd can't be given directly ? If I have the Kd value of a certain compound at hand, I have to set the values of KOC and fOC, then the model would calculate Kd internally by multiplying KOC with fOC. Is that right?