I found this on propylene glycol, NOT RV antifreeze itself:

12 ECOLOGICAL INFORMATION
Acute Toxicity:
Fish: Low toxicity: LC/EC/IC50 > 40,000 mg/l
Aquatic Invertebrates: Low toxicity: LC/EC/IC >4,000 mg/l
Algae: Low Toxicity: LC/EC/IC >15,000 mg/l
Microorganisms: Low Toxicity: LC/EC/IC >20,000 mg/l
Mobility: Dissolves in water. If product enters soil, it will be highly mobile and may contaminate ground water.
Persistence/degradability: Readily biodegradable.
Bioaccumulation: Does not bioaccumulate significantly.

The complete msds for propylene glycol based RV antifreeze can be found here:
http://www.bosslubricants.com/pdfs/msds/Anti%20Freezes/BOSS%20RV%20ANTIFREEZE.pdf

A section of the msds, relevant to the discussion:



ECOTOXICOLOGY: based largely or completely in information for similar material, i.e. propylene
glycol. Material is practically non-toxic to aquatic organisms on an acute basis (LC50 greater than
100mg/L in most sensitive species.
Acute LC50 for fathead minnow (Pimephales promelas) is 4600-54900 mg/L.
Acute LC50 for guppy (Poecilla reticulata) is greater than 10000mg/L.
Acute LC50 for water flea Daphine magna is 4850-34400 mg/L.
Acute LC50 for rainbow trout (Oncorhynchus mykiss) is 44mL/L (about 44000 mg/L).

"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.