Powdered "free" silica is not in and of itself toxic. Silicone Dioxide (SiO2) is actually pretty inert at room temperatures. However breathing free silica over the long term can cause all sorts of respiratory issues because of it's physical characteristics, chief among them being silicosis (similar to asbestosis). The resulting scaring can cause decreased lung function, which if severe enough can obviously lead to death. As a potter, it is something I have to be aware of. While I don't put on a hazmat suit just to look into a bag of pottery material, but I sure as heck put on a respirator (not a cheap face mask) if I'm mixing clay or measuring out glaze ingredients. Now I'm not saying that you will never have problems if you inhale a few Milligrams of silica every once in a while, or that you definitely will have problems if you purposely inhale a Kilogram a week. Some people just don't do well, while others do. Same thing with smoking, one smoker who consumed 3 packs a day for 50 years has squeaky clean X-rays, while the next person smoked for a couple of years 30 years ago, and is now in treatment. Go figure. Now it is my understanding (I do not KNOW this) that the DE used in pool filters is chemically treated, and actually IS toxic. I also know that DE filters were/are used in the aquarium trade, and some of the aquarium critters are pretty sensitive, but I don't know if they use pool DE or not. Bottom line is if you get some incidental exposure such as driving down a dry dirt road, it should not be a big deal if you don't already have lung issues. If you shuffle through chicken litter that has lots of free silica in it day in and day out for the next 20, 30, 40, or more years, I would wear a respirator. The truth is that breathing in copious amounts of just about any fine particulate matter over the long term can cause problems. Everything in moderation. Be safe and get food grade, it's just not worth the potential risks to you, your family, or your chickens.
Swamp
