Don’t know if any of this information will be helpful or if someone has already sent something but here goes with some data that I found - First NOTE - this information is coming from the Animal Damage Control Program

If you have access the publication is US Dept of Agriculture, APHIS January 1993 - Animal Damage Control Control Program - Supplement to the Draft Environmental Impact Statement - Vol. 1 & 2.

Under the section - environmental Consequences - Environmental Fate Characteristics by Active Ingredient (basically this publication is numerous table and study results)

Zinc Phosphide - Mobility (Soil, Water) insoluble & generally immobile. Under moist conditions is soil, z.p. breaks down to PH3, which is released into the atmosphere or converted to phosphates & zinc complexes.

Bioaccumulation - does not accumulate in animal tissue

Persistence (Soil, Water) - moderate to low; decomposes within 30 days,
Phosphine gas is converted to harmless phosphates.

This next set of data is taken from the LABELS which must be present on the delivery mechanism. In this case the delivery is either steam-rolled oats or rolled oat groats:

Environmental Hazards - This product is toxic to wildlife and fish. Birds and other wildlife feeding in treated areas may be killed. Use with care when applying in areas frequented by wildlife or adjacent to any body of water. Keep out of lakes,ponds, or streams. This product shall not be applied over bodies of water, in areas inhabited by livestock, or where a hazard exists to rare or endangered species. Do not contaminate water by cleaning of equipment of disposal of wastes.

Endangered Species Considerations

Whooping cranes - Do not use this product 30 days prior to arrival and 30
days after the whooping crane leaves its known critical habitat.

Attwater’s Greater Prairie Chicken - (pretty much same as above)

Yellow-Shouldered Blackbird & Puerto Rican Plain Pigeon - Do not use in critical habitat except in tamper-proof bait boxes - listed various specific locations.

Utah Prairie Dog - Do not use this product in critical habitat.

Think you can get the picture - If an animal ingests the poison they’ll be dead.

Some general information " most widely used rodenticide - toxic effects from single dose, but because of its offensive taste & odor, prebaiting with untreated bait is usually required to achieve consumption of a lethal dose. (This seems like there could be animals which leave without eating a lethal dose - but they would be suffering from a near fatal dose) At the time of publication of this book it looks like there were 13 states 1988-1991 using zinc phosphide.

Toxicology - 2 to 15 Xs more toxic to rodents than to carnivores. Secondary poisoning to predators and raptors is possible, especially if the chemical is not assimilated into the target species.

Metabolism - Following ingestion, the transformation of Zn3P2 to phosphine gas in the stomach appears to dominate the toxicity of this compound. Phosphine is a highly toxic gas that elicits its effect in the liver & lungs. The PH3 most likely accounts for theacute toxicity of z.p. Death usually results from asphyxia. The time between ingestion and death is generally about 30 hours!

More information about this and other stuff goes on for the next 8-9 pages. But I think you get the point. It’s bad for the animals and the environment.