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It could have been in the lead in the alloys that were used in the dishes and other eating utinsles oat the time. It used to be thought tomatoes were poinsonous. It turn out the tomatoes caused sickness because the acid in them extracted the lead in pewter and other alloys, causing them to get in the food and cause sickness.
I may be wrong, but I thought tomatoes were a New World product, like potatoes, maize and popcorn.
If this is true, then it's unlikely the ancient Romans would have had tomatoes to cook in their lead/pewter utensils. They may have cooked other acidic foods in lead pots, however. And it's true that tomatoes were considered poisonous in many areas until the last century.