Water Quality
2.
Aquatic Life
2.1
Freshwater
To protect
freshwater aquatic life from adverse effects, the concentration
of chlorate should not exceed 30 mg/L in the water column.
Rationale:
Chlorate appears to be non-toxic (LC50 is greater than 100 mg/L)
to freshwater life. Five species of insects were exposed for 10 days to chlorate
up to 100.0 mg/L. The 48-hour LC50 for Daphnia magna was
estimated at 3162 mg/L. For freshwater algae the lowest effect level, an LOEC
for growth inhibition in Chlorella vulgaris, was 334 mg/L chlorate
at 28 mg/L nitrate. The lowest effect level, a
24-hour LC50 to an aquatic invertebrate (the water flea, Daphnia
magna) was 880 mg/L of chlorate. The lowest effect level, a 96-hour LC50
to a freshwater fish, (larval cherry salmon, O. masou) was 863 mg/L
of chlorate at an unspecified nitrate level.
For freshwater
life a guideline is proposed to protect the most sensitive
species, which appear to be green algae. The recommended guideline
is 30 mg/L of chlorate ion (37 mg/L sodium chlorate), based
on applying a LOEL to NOEL factor of 0.1 results to the LOEL
of 334 mg/L, resulting after rounding in a guideline of 30
mg/L.
2.2 Marine
To protect
marine aquatic life from adverse effects, the concentration
of chlorate should not exceed 5 µg/L in the water column.
Rationale:
For marine life, the guideline is set to protect the most sensitive species,
brown algae. These include the kelps (Macrocystis) and Fucus (bladder
wrack). This guideline is based on the NOEC of 5 µg/L chlorate from a
six-month chronic study on the growth of Fucus vesiculosus. The LOEC
for chlorate from this study was 15 µg/L and the EC50 was 100 µg/L.
The NOEC was accepted as the guideline since the reported values from these
studies confirm the standard 20:1 ratio of EC50 (or LC50) to NOEC that is generally
applied in deriving guidelines.
