306
alike among different trophic level species. For example, the highest concentrations
of PFOA and in invertebrates [37] are similar in range, whereas in reptiles [38], fish
[39], mammals [40, 41] and birds [42, 43] the maximum concentration of PFOS is
up to 3 times of magnitude is higher in comparison with PFOA. The lower potential
of bioaccumulation of PFOA may be due to the length of the perfluorocarbon chain
and difference in the functional group in PFOS compared with PFOA [32]. Due to
the phase out of PFOS, in a recent time period, PFSA concentrations showed declining rates in biota in 2002 [44–46]. However, no clear trend has seen in the other
PFASs concentrations, for example, long-chain PFCAs are rising in concentration
depending on trophic level, the compound, and different geographical location [47].
Therefore it is considered that PFAS is persistent as a whole in the environment,
while precursors of PFAS can be degraded to PFSAs and PFCAs [10]. In the aquatic
ecosystem continuous introduction of PFAS can consequence in constant exposure
of such chemical compounds for those organisms that are present in the depth of
discharges. From these observations, it is concluded that aquatic organisms suffering discharges of waste water and other sources of PFAS are more exposed to these
hazardous chemicals [48]. Only a few numbers of studies deal with implications of
this fact over various generations [49]. Survival of juveniles was assessed by Drottar
and Krueger in 2000 (over 48 hands 96 h) released from Daphnia Magna (freshwater Cladocera) that was exposed with PFOS and Mysidopsis Bahia (marine Mysida)
in medium contaminated with the same concentration of PFOS as the media adults
had been living. After this short time exposure of PFOS shift insensitivity indications were not exhibited by Daphnia and Mysidopsis. Studies were conducted with
invertebrates, Japanese medaka (Oryzias latipes) was exposed to either PFOS or
PFOA (in the mgL1 range) discharged offspring that showed a high rate of mortality
and alterations in the histopathological pattern even after the hatching in controlled
medium (PFAS-free) compared with the progeny discharged from control animals.
If the exposure was continued with F1 generation the effect was more pronounced
[50]. So, it is concluded that if a species exposed to PFOS or PFAS for one generation the effects can be observed on the next generation. If the aquatic ecosystem
continuously being exposed with polyfluoroalkyl and perfluoroalkyl substances the
next generations will continuously show after effects, studies should be conducted
to assess the potential implications over multiple generations particularly for those
generation having short generation time, e.g. Daphnia or Chironomus. Experiments
should be performed to analyze multiple generations to see whether hazardous
effects persist even in PFAS-free media (controlled conditions) by simulating the
species migration to nearby unpolluted aquatic media. Overall, hazardous results of
PFASs should be evaluated considering a continuous exposure to the environment.
Occurrence and Exposure in Relation to Humans
In the past short-chain, PFAS was found in minor constituents of long-chain PFAS
or as a contaminant but in recent times utilization of short-chain PFAS is increasing
day by day as an alternative for C8-PFAS. Still, it is largely unclear which source of
S. G. Niazi et al.
alike among different trophic level species. For example, the highest concentrations
of PFOA and in invertebrates [37] are similar in range, whereas in reptiles [38], fish
[39], mammals [40, 41] and birds [42, 43] the maximum concentration of PFOS is
up to 3 times of magnitude is higher in comparison with PFOA. The lower potential
of bioaccumulation of PFOA may be due to the length of the perfluorocarbon chain
and difference in the functional group in PFOS compared with PFOA [32]. Due to
the phase out of PFOS, in a recent time period, PFSA concentrations showed declining rates in biota in 2002 [44–46]. However, no clear trend has seen in the other
PFASs concentrations, for example, long-chain PFCAs are rising in concentration
depending on trophic level, the compound, and different geographical location [47].
Therefore it is considered that PFAS is persistent as a whole in the environment,
while precursors of PFAS can be degraded to PFSAs and PFCAs [10]. In the aquatic
ecosystem continuous introduction of PFAS can consequence in constant exposure
of such chemical compounds for those organisms that are present in the depth of
discharges. From these observations, it is concluded that aquatic organisms suffering discharges of waste water and other sources of PFAS are more exposed to these
hazardous chemicals [48]. Only a few numbers of studies deal with implications of
this fact over various generations [49]. Survival of juveniles was assessed by Drottar
and Krueger in 2000 (over 48 hands 96 h) released from Daphnia Magna (freshwater Cladocera) that was exposed with PFOS and Mysidopsis Bahia (marine Mysida)
in medium contaminated with the same concentration of PFOS as the media adults
had been living. After this short time exposure of PFOS shift insensitivity indications were not exhibited by Daphnia and Mysidopsis. Studies were conducted with
invertebrates, Japanese medaka (Oryzias latipes) was exposed to either PFOS or
PFOA (in the mgL1 range) discharged offspring that showed a high rate of mortality
and alterations in the histopathological pattern even after the hatching in controlled
medium (PFAS-free) compared with the progeny discharged from control animals.
If the exposure was continued with F1 generation the effect was more pronounced
[50]. So, it is concluded that if a species exposed to PFOS or PFAS for one generation the effects can be observed on the next generation. If the aquatic ecosystem
continuously being exposed with polyfluoroalkyl and perfluoroalkyl substances the
next generations will continuously show after effects, studies should be conducted
to assess the potential implications over multiple generations particularly for those
generation having short generation time, e.g. Daphnia or Chironomus. Experiments
should be performed to analyze multiple generations to see whether hazardous
effects persist even in PFAS-free media (controlled conditions) by simulating the
species migration to nearby unpolluted aquatic media. Overall, hazardous results of
PFASs should be evaluated considering a continuous exposure to the environment.
Occurrence and Exposure in Relation to Humans
In the past short-chain, PFAS was found in minor constituents of long-chain PFAS
or as a contaminant but in recent times utilization of short-chain PFAS is increasing
day by day as an alternative for C8-PFAS. Still, it is largely unclear which source of
S. G. Niazi et al.