The demand for rare earth elements
(REEs) has increased since the
1990s leading to the development of many mining projects worldwide.
However, less is known about how organisms can handle these metals
in natural aquatic systems. Through laboratory experiments, we assessed
the chronic toxicity and subcellular fractionation of yttrium (Y),
one of the four most abundant REEs, in three freshwater organisms
commonly used in aquatic toxicology:
Daphnia magna
,
Chironomus riparius,
and
Oncorhynchus mykiss
. In bioassays using growth as
an end point,
C. riparius
was the only
organism showing toxicity at Y exposure concentrations close to environmental
ones. The lowest observable effect concentrations (LOECs) of Y assessed
for
D. magna
and
O.
mykiss
were at least 100 times higher than the Y concentration
in natural freshwater. A negative correlation between Y toxicity and
water hardness was observed for
D. magna
. When exposed to their respective estimated LOECs,
D. magna
bioaccumulated 15–45 times more Y
than the other two organisms exposed to their own LOECs. This former
species sequestered up to 75% of Y in the NaOH-resistant fraction,
a putative metal-detoxified subcellular fraction. To a lesser extent,
C. riparius
bioaccumulated 20–30% of Y in
this detoxified fraction. In contrast, the Y subcellular distribution
in
O. mykiss
liver did not highlight
any notable detoxification strategy; Y was accumulated primarily in
mitochondria (ca. 32%), a putative metal-sensitive fraction. This
fraction was also the main sensitive fraction where Y accumulated
in
C. riparius
and
D.
magna
. Hence, the interaction of Y with mitochondria
could explain its toxicity. In conclusion, there is a wide range of
subcellular handling strategies for Y, with
D. magna
accumulating high quantities but sequestering most of it in detoxified
fractions, whereas
O. mykiss
tending
to accumulate less Y but in highly sensitive fractions.