You can't find anything about toxicity of Hedera (Ivy) in the environment because it isn't toxic, unless you eat it. This is true of over 50% of plants commonly grown in gardens in the northern hemisphere, which is why it's important to instruct children in regard to consuming any leaves and particularly berries they may find growing.
One issue that some people have occasionally (I am one of them) is cutting it with a hedge trimmer - this can irritate the airways in some asthmatics, though cutting with secateurs or loppers reduces this problem. Generally, it seems the cause of airway irritation is largely the dust and other particles which have collected on the ivy leaves and stems - during cutting with electric equipment, this is all flying about and you're breathing it in. It's also possible that the sap irritates the airways during cutting, so wearing a mask during major cutting back IF you are sensitive is advisable. Some people may experience contact dermatitis from the sap, so its wise to keep the skin covered as far as possible during cutting back by wearing gloves and long sleeves, though I've never found skin contact with it to be an issue.
If you are intending to allow an ivy to cover a fence, you will need to trim it back more or less flat against the fence annually or biennially as it matures to reduce the weight on the fence and keep it under control; ensure the fence is in good condition prior to planting. If the fence is wooden, it will, over time, rot beneath the ivy and may collapse under the weight, but not usually for ten years or more if kept trimmed back. Unfortunately, trimming it back usually means the flowers get removed, so if you can, leave trimming it back till the flowers are finished, or do it in spring. The blooms are not particularly attractive to us, but they are a valuable source of nectar for pollinating insects such as bees when there is little else available in autumn.