Before taking supplements you should have a blood test for the level you already have in your body. .1 ppm could mean the difference between OK and Toxic. I have learned that so much of our food already has more than enough selenium. You could already be toxic from that.
I learned all this from my herd of pigs which went Chronically Toxic with just eating their regular ration made by a big company. The added selenium was within FDA law, but the grains themselves were toxically high. Nobody regulates the natural selenium level in grains or any other food, only the Addition of selenium.
Grains that are grown in high selenium soils and shipped everywhere, you never know what state your grains are coming from. South Dakota and Nebraska just to mention two with very high selenium levels in soil.
You know the meat is high because of the animals eating the high selenium grains. Also, what about the cows milk and soy milk? Both are high in selenium. Have your kids tested.
Symptoms vary by individual, symptoms mimic many other diseases. Symptoms often don't look related. If you die of liver failure you won't have to worry about prostate cancer. Doctors are so clueless. If you run your body at "High Normal" level, you easily run the risk of becoming Chronically Toxic at any given moment.
Agitation and agressive behavior, excessive salivation, constipation or diahreah, central nervous system problems, liver or kidney problems, brittle hair and nails, reproductive problems, muscle weakness ( including uterine muscles), numbness, garlic breath, If you can think of it, selenium can cause it. The list of symptoms is too long for me to list here. You may only have one of the symptoms.

This is a very dangerous mineral. Get tested first.