TY - JOUR

T1 - Response to comment on "Screening criteria for long-range transport potential of organic substances in water"

AU - Zarfl, Christiane

AU - Scheringer, Martin

AU - Matthies, Michael

PY - 2013/4/2

Y1 - 2013/4/2

N2 - In his comment on our article “Screening Criteria for Long-Range Transport Potential of Organic Substances in Water”,(1) Sierra Rayne points out that single compounds out of the list of “4069 non-ionic organic compounds” may be ionizable. This may be and is, in fact, the case, but these substances will only dissociate to a specific amount, which is a consequence of the selection process out of the Canadian Domestic Substance List (CDSL). We selected those substances as “non-ionic”, for which the neutral fraction is larger than 95% in the environmental relevant pH range of water from 4 to 10. This is the same procedure as described in more detail in our article “Identification of substances with potential for long-range transport as possible substances of very high concern”(2) which results in a list of 5091 organic and (to more than 95%) nonionic compounds from the CDSL. This list of substances can easily be derived from the original CDSL by, for example, applying the SPARC online calculator (same as Mr. Rayne did for a few of the compounds listed in the SI) to the organic substances (tagged as “organic” within the CDSL). In addition, for analyzing the long-range transport of substances in water those (4069) compounds were selected “which are not persistent in water (t1/2(W) < 40 d) but exceed the half-life criterion of 10 days in freshwater” (see ref 1, p 10079, last paragraph, first sentence). We are convinced that the publication of the total list of 4069 substances is not of an additional value to the reader, but can, of course, be provided on request. Sierra Rayne also underlines that the Kaw of PFOS should be “essentially zero”, and that therefore, this compound “will be present effectively entirely in water”. We do not see a contradiction to our results which indicate the same environmental behavior, that is, Kaw of 2 × 10–6 which is close to zero (effectively, a distribution coefficient can never be zero) such that the substance mass (mainly) distributes into the water compartment (Figure 1 of our article). Same as the value for the log Kow the substance properties for PFOS, which are displayed in Table S1 of our article, are cited from the Risk Profiles of the Stockholm Convention. This is mentioned in the heading of our table.

AB - In his comment on our article “Screening Criteria for Long-Range Transport Potential of Organic Substances in Water”,(1) Sierra Rayne points out that single compounds out of the list of “4069 non-ionic organic compounds” may be ionizable. This may be and is, in fact, the case, but these substances will only dissociate to a specific amount, which is a consequence of the selection process out of the Canadian Domestic Substance List (CDSL). We selected those substances as “non-ionic”, for which the neutral fraction is larger than 95% in the environmental relevant pH range of water from 4 to 10. This is the same procedure as described in more detail in our article “Identification of substances with potential for long-range transport as possible substances of very high concern”(2) which results in a list of 5091 organic and (to more than 95%) nonionic compounds from the CDSL. This list of substances can easily be derived from the original CDSL by, for example, applying the SPARC online calculator (same as Mr. Rayne did for a few of the compounds listed in the SI) to the organic substances (tagged as “organic” within the CDSL). In addition, for analyzing the long-range transport of substances in water those (4069) compounds were selected “which are not persistent in water (t1/2(W) < 40 d) but exceed the half-life criterion of 10 days in freshwater” (see ref 1, p 10079, last paragraph, first sentence). We are convinced that the publication of the total list of 4069 substances is not of an additional value to the reader, but can, of course, be provided on request. Sierra Rayne also underlines that the Kaw of PFOS should be “essentially zero”, and that therefore, this compound “will be present effectively entirely in water”. We do not see a contradiction to our results which indicate the same environmental behavior, that is, Kaw of 2 × 10–6 which is close to zero (effectively, a distribution coefficient can never be zero) such that the substance mass (mainly) distributes into the water compartment (Figure 1 of our article). Same as the value for the log Kow the substance properties for PFOS, which are displayed in Table S1 of our article, are cited from the Risk Profiles of the Stockholm Convention. This is mentioned in the heading of our table.

KW - Chemistry

KW - Environmental Monitoring

KW - Organic Chemicals

KW - Water

U2 - 10.1021/es4008867

DO - 10.1021/es4008867

M3 - Comments / Debate / Reports

C2 - 23444973

VL - 47

SP - 3544

EP - 3544

JO - Environmental Science & Technology

JF - Environmental Science & Technology

SN - 0013-936X

IS - 7

ER -