except for the one that looks like an acetylene bottle those don't look in too bad a condition. Whats in them - chlorine? Except for the pointy ones they look like gas bottles, not bombs
As for the mustard gas "pots" at Chilmark - if they've been bleached out they should be safe, especially after all this time. Don't worry about effects from the chlorine bleach - that will be well neutralised by the groundwater by now.
The bigger risks come from two problems: shells which were deployed for hidden storage during WW2 and then lost. I seem to remember a few mustard shells surfaced on a hillside in Lancashire near Clitheroe ten years or so ago. The site had been a TA training range during WW2
And then there are the undocumented production sites and shell filling plants. For instance local tradition has it that there was a gas shell filling plant in Lancaster during WW1 - but there are no records of it: everything was kept secret. Its possible to make educated guesses, but no-one knows. One possible site (which was later used for making arsenic products for horticulture) has had flats built on it