Supplies MSC and Wildlife?

MSC shouldn't be sprayed in enclosed spaces without ventilation because it becomes concentrated and that concentration of chemicals isn't good for anything's health. Spraying outside the wind and air will greatly reduce the concentration to non toxic levels. As along as you avoid getting it on anything living it shouldn't have any impact on them. And you can use a large cardboard box or spray booth so the over-spray doesn't get on anything. Then the aerosol chemicals will just disperse in the outside ventilation.

 

Something I do to minimize overspray is to place the item inside a large-ish box and spray with the wind at my back and into the box so the sealant goes toward the box (where it isn't going on the item).

For something still relatively inexpensive with even less overspray I believe people have made fully enclosed spray boxes using a very large box, some waterproof gloves and some kind of plastic or acrylic sheeting. If you do go this way it's good to make sure the box is deep enough to accommodate the sealant's recommended spray distance and to make sure the gloves are sturdy and well secured. The ones I have seen look a bit like a cardboard version of those boxes with the gloves inside that premature babies are cared for in at the hospital.

For the full price option there are ventilated spray boxes with filters and fans for sale on Ebay and probably at some hobby shops that sell scale model painting kits. Good luck with the search!

 

It's very sweet of you to worry about the wildlife in your garden! But as others have said, the issue with MSC/aerosols in general is the concentration issue - the reason it should only be sprayed in a well ventilated area is that the chemicals aren't able to disperse properly in a confined space with little to no air movement, which makes you breathe in enough for the dosage to be toxic. In theory, the second the mist gets outside, it should disperse enough that the dosage of toxins would be minimal, but not invisible. All this being said, animals are generally much more sensitive to smells and sounds, and many would likely immediately leave upon detection of a human or unusual sound, such as a spray can (Notice it kind of sounds like a snake or a cat hiss? Small animals that are preyed upon by such animals will often immediately leave when they hear it.) I think as long as you observe the proper protocols to protect yourself, and make sure you aren't spraying directly on anything living (be it plant or animal), no harm should come to anyone involved.

 

To be honest the only way you're going to minimise environmental impact is by, as suggested, making a spray booth of some form to catch the overspray.

While the 'smell' may disperse the actual spray contents do not, they will eventually land on a surface and pollute it as they consist of various chemical compounds and plastics. It is a sealant after all, coating surfaces is what it's made for so you are right to be concerned about the long lasting implications when it lands on plants, rocks, soil, etc. The odds on chances are that it will by natural erosion and movement of organisms be ingested by wildlife or even humans if veg, fruit and herbs are grown anywhere close by.

 

I use a home made box, to avoid the sealant ending up in the wrong place.

My very low tech solution is a large cardboard box laying on it side with the opening towards me. I have covered the front with a large clear garbage bag that is taped down around the top and left side of the box so that the rest hangs down as a large loose flap.
When I spray Ii slide my arm (can in gloved hand, wearing long sleeved work sweater) under the bag and into the box.
The overlap is pretty big, so very little spray can escape.
The clear plastic lets me see what I am doing.
When I have finished I slide my arm out and tuck the extra plastic in under the box and leave it outside to dry. That way I don't get any dust stuck in the sealant even if it's windy.
With use, sealant (and paints, I do use the same box for any aerosol job) build up on the plastic and it needs to be replaced, but other than that it's basically maintenance free.