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I moved into a new house (built 1979) this past fall and I would like to convert some of the grass area to a vegetable garden. I don't know how the previous owners took care of their lawn, but is there any chance of of unsafe chemicals still hanging around in the soil?
I'm thinking of just normal lawn care products. Do they dissipate over time? If so, how long?
From the current state of the grass, it does not appear they did anything special to it.
If you're really anxious about it, do as Evol Gate suggests, but to answer your query about timespan of activity for lawn care/treatment products, the longest acting one I can think of is one that might be used in the Autumn. This contains a small amount of nitrogen and sometimes a chemical to retard the growth of moss, and its length of activity is between 4-6 months at the most. If the grass you have looks in wonderful condition, with no weeds or moss or anything else, and no bald patches, then it's likely chemical treatments have been used. If it looks like most 'lawns', that is the opposite of what I've just described, then it's likely nothing much has been applied to it, and particularly not an autumn feed. Certainly, any growing season (April through to early July in the UK) products used last year will have long since dissipated. This answer assumes you're not in Australia...
As you mentioned there has been grass growing on the area, which implies that the soil there is not badly contaminated. Since you want to grow vegetables out there, therefore it isn't worth taking a risk. The best way to check this would be grow few fast growing vegetable plants like tomatoes (sow the seeds of a tomato, don't plant an already grown plant) in some various areas of the garden. It will hardly take a month and a half for them to give you tomatoes. Take these tomatoes to any laboratory to have them tested. The lab results will definitely tell you whether the tomatoes have any sort of contamination or they are safe for health.
I would recommend using raised beds so that you don't get contaminated with whatever may be in the ground. I helped build a community garden and we had to used raised beds because of the chemicals that were in the ground. You can never be too sure with things like this so it's best to not use the dirt in the ground because health regulation weren't followed diligently back in the 1970s. There are lots of carcinogens that can cause cancer.
