The paper itself may be harmful to fish or other water life as an inert and non-nutritional object that could be mistaken for food, but I did not find any information about toxicity. However, the chemical residues which are released into the atmosphere and may also be on the paper after the explosion of the firework could be toxic. The colors of (modern) fireworks are due to the burning of various compounds to produce metal chlorides which glow. Some of the unburned metals are toxic to animals (and humans), as are some of the products of the chemical reactions. Scientists are aware of the problems posed by fireworks and are developing environmentally friendly alternatives to the traditional, but harmful, designs and chemistry. For example, some shells are now made of a type of plastic which completely burns up instead of leaving paper that pollutes waterways and hurts fish.

There is no universal recipe for the paper packaging of a firework. Therefore any general discussion of its toxicity would be difficult.

Two patents patent 1 , and patent 2 showed that Direct Red is used as a dye for firework papers.

Based on the safety data sheet (SDS) from, Sigma Aldrich the dose needed to kill half of the test animals within a time period (LD50) for Direct Red is greater than 5g per kilogram body weight. It is less toxic than table salt (rat oral LD50 3g/kg) and vitamin A (rat oral LD50 2g/kg). Direct Red is also not a known carcinogen or mutagen.

Direct Red alone is probably not that toxic. However, this example should be sufficient to demonstrate that any discussion of toxicity is highly specific to the chemical in question. Without a clear knowledge of the material, such discussion is difficult.

This depends on the dye that is used to make the paper red. I don't know what this dye is, and multiple dyes could be used, and some of them more poisonous than others.

This is an interesting link to read.