The temporal tren
ds of perfluoroalkyl compoun
ds (PFCs), inclu
ding C7−C15 perfluorocarboxylates (PFCAs), perfluorosulfonates (PFSAs) an
d hepta
decafluorooctane sulfonami
de (PFOSA), were
determine
d in lake trout collecte
d between 1979 an
d 2004 from Lake Ontario. The average concentrations of total PFSAs (
![](http://pubs.acs.org/images/entities/plusmn.gif)
stan
dar
d error of the mean; range) increase
d from 20 ng g
−1 wet weight (
![](http://pubs.acs.org/images/entities/plusmn.gif)
4; 8−26) in 1979, peake
d at 70 ng g
−1 (
![](http://pubs.acs.org/images/entities/plusmn.gif)
7; 58−91) in 1993, an
d were 46 ng g
−1 (
![](http://pubs.acs.org/images/entities/plusmn.gif)
10; 30−83) in 2004, with perfluorooctane sulfonate (PFOS) as the most abun
dant PFC. The PFCAs exhibite
d similar temporal variation, with concentrations increasing from 1.4 ng g
−1 (
![](http://pubs.acs.org/images/entities/plusmn.gif)
0.1; 0.9−1.9) in 1979 to 9.4 ng g
1 (
![](http://pubs.acs.org/images/entities/plusmn.gif)
3.1; 3−17) in 1988, an
d were 6.8 ng g
−1 (
![](http://pubs.acs.org/images/entities/plusmn.gif)
1.0; 4.5−9.8) in 2004. In
divi
dual mean PFCA concentrations varie
d between 0.2 an
d 2 ng g
−1 (wet weight). Perfluoro
decane sulfonate (PFDS) an
d PFOSA were the only compoun
ds showing a
declining tren
d in the past
deca
de, after reaching a peak value in 1993. Branche
d C11 an
d C13 PFCA isomers were
detecte
d in the lake trout an
d confirme
d in Niagara River suspen
de
d se
diments, with tren
ds in both matrices suggesting that
declining emissions or use of pro
ducts containing these isomers in part account for the observe
d PFCA tren
ds in the mi
d-1990s. However, the most recent samples, comprise
d almost exclusively of linear isomers, in
dicate that current PFCA sources to Lake Ontario result from the telomerization process of linear telogens.