With sales and use of consumer fireworks now legal in Maine, careful detonation and disposal is important to keep users, spectators and our environment safe. The Maine State Fire Marshal’s office website has information on State and local fireworks laws and regulations.
Always think about safety when using fireworks.

• Use fireworks outdoors only.
• Obey local laws. If fireworks are not legal in your community, do not use them.
• Always have water handy (a hose or bucket) and follow manufacturer’s instructions.
• Never relight a “dud” firework. Wait 20 minutes and dispose of properly.
• Use common sense.

Fireworks and Air Quality

Like any combustion, fireworks produce a variety of air pollutants including particulates. The compounds used to produce fireworks colors contain metals which enter the surrounding air when the fireworks explode and later settle. Fireworks that combust near ground level can have short-term, limited impacts on air quality and should be used with care near sensitive groups such as children, the elderly or people with asthma or respiratory disease.

The particulates and other pollutants produced by fireworks disperse quickly and to date have not exceeded ambient air quality standards in Maine. Maine DEP monitors daily and hourly air quality at multiple locations across the State.

Fireworks and Water Quality

For visual effect, fireworks are often detonated over or near water. As noted above, fireworks may contain a variety of pollutants such as certain metals that can also contaminate water. However, the amount of these potential contaminants is relatively slight in comparison to the volume of water and since detonation typically occurs well above the water surface, pollutants are dispersed by the wind with little falling directly on the water. Users should remove and dispose of any visible debris or litter from shell materials. Fireworks should never be detonated in the water since the concussion effect could kill nearby fish or other aquatic life.

Fireworks and Safe Disposal

If you have unused, misfired or “dud” fireworks, following these safe disposal steps will help ensure the protection of you, your family and waste haulers and handlers:

• Completely submerge fireworks in a large bucket of water and soak until thoroughly saturated. This may take 15 minutes for small fireworks or as long as overnight for larger ones.
• Double wrap the completely soaked fireworks in plastic wrap or two plastic bags so they do not dry out.
• Place the double-bagged fireworks in the household trash or take them to your local solid waste facility.
• You can contact your local fire department or solid waste facility as other disposal options may be available in your community.

If you plan to store unused fireworks that have not yet expired, keep them in a cool, dry place such as a garage and out of the reach of children. Never place fireworks on top of an electrical appliance, such as a refrigerator or freezer.  The appliance could be struck or damaged through extreme weather events such as lightning or power surges, resulting in the possible ignition of the fireworks.

Source: https://www.maine.gov/dep/how-do-i/how-do-i.html?id=440736