Have just been sent this link to an article in Sunday's Observer about a Dow herbicide that is used on grass getting into the food chain via silage and horse manure - it damages/kills homegrown fruit and veg (apart from courgettes, oddly) and it is recommended by the RHS and others that any dodgy fruit or veg in gardens or allotments should not be eaten as the safety (or lack of) of this chemical is unknown in the food chain.