Galvanized troughs  make excellent gardening containers.  Plants grow well in them, and they save alot of bending over in the garden.  The only problem when growing vegetables is that over time small amounts of zinc and cadmium can leach out from them.  Keep in mind that before the age of plastic, galvanized water pipes were the norm.  Zinc is a necessary mineral in small amounts.  The main risk is from contact with acidic food, like pickles. 

This information from OAR Food Sanitation Rules, page 46. "4-101.15 Galvanized Metal, Use Limitation.* Galvanized metal may not be used for utensils or food-contact surfaces of equipment that are used in contact with acidic food."  might help you put it in perspective.

One solution is to use a plastic liner or panels on the walls of the trough.  Using them on the bottom  can interfere with drainage.

Troughs have a drainage hole so when used as a watering device, the tank can be drained.  You might want to add more drainage by drilling additional holes.   Adding gravel to the bottom will help maintain drainage.  Another tip is to place the trough on a base of blocks.  This not only helps keep the drainage holes open, but can provide a nice cool spot for frogs and lizards.  They'll eat the insects in your garden.

With a little planning you can have a safe, easy to use raised bed for your plants.  The glue is probably an epoxy-type glue and should cause no problems.  This article has good, practical advice for using galvanized containers for vegetable gardening, Growing Vegetables in Galvanized Containers  http://solanomg.ucanr.edu/newsletters/Seeds_for_Thought64596.pdf.