I should also add that Material Safety Data Sheets (MSDS) are created for the work force, as in those workers who handle these goods on a regular basis, and who may be exposed to elevated levels of these chemicals, on a regular basis. There is an MSDS for almost every chemical substance on the planet, including the main component found in household vinegar, and they all appear to be very alarming on the surface.
Many household goods contain these same chemical substances, even the ones found in API water conditioner. Given the small amounts of EDTA used in water conditioners, I doubt that toxicity would be much of an issue, unless you are placing fish into a container that contains 100% full strength water conditioner, which isn't likely. I believe that the The LC50/96-hour values for fish are over 100 mg/l, which simply means that the EPA do not want manufacturers etc dumping EDTA into the local stream/lake - but does not equate to it being harmful to aquatic fish/plants when used accordingly, such as products created for aquarium use.
Keep in mind that you & your family most likely use products containing substances such as EDTA on a daily basis more than you realize.
As an example, check out the list in the link below for common household goods, including baby shampoo, that contain Tetrasodium EDTA. (pet care products are listed at the end)
http://householdproducts.nlm.nih.go...query=edta&searchas=TblChemicals2&prodcat=all
Ditto to sodium thiosulfate which has been used by aquaculture facilities for longer than most people on this forum have been alive.
Is it safe, absolutely - but like most chemicals you need to use some common sense when working with them, especially if you are a factory worker that may be exposed to high levels on a constant basis. You don't want your children drinking water conditioner, or snorting it, or soaking their hands in it, anymore than you want them inhaling the dust from silica based play sand. That doesn't mean that these substances when used properly are going to be harmful to your fish, any more than play sand is.
The exact same safety precautions would apply to acetic acid, the main chemical component found in household vinegar.
http://www.sciencelab.com/msds.php?msdsId=9922769
Looks pretty alarming when viewed via a MDSD, right? Yet millions of people not only use vinegar as a cleaner, many ingest it via their diet.
Fish & Chips anyone? Considering the info found in the MSDS - half of the UK should be dead by now.
Most chemicals are dangerous at some level, especially to young children. Vitamin A, Iron supplements, etc can also be lethal to a toddler - does that mean we ban vitamins? Obviously not, but common sense should be applied as to where & how ALL of these products are stored, and used.
No need to go off the deep end over any of this, all that's required is a healthy dose of common sense.