After talking to a scientist who works on a family of worms called C. Elegans (another invertebrate), she said that lead does have several effects that can be monitored. In the worms, lead can reduce the brood size and generation time; however, that may be difficult to monitor with slugs, since their reproduction time is slightly longer. Lead can also increase resistance to the de-worming drug levamisole. I'm not sure if this drug also works on slugs, but it may? The metal can also reduce lifespan and impair memory of thermosensation. So one example may be to see if lead can change how a slug would respond to heat.

I hope that this is helpful, thats a fantastic question.

The easiest way to test lead on the slugs would be to add it to their food.I've attached 2 articles on lead toxicity in slugs where they added lead to the food. These are primary research papers and the writing is very dense and full of complicated details and techniques. Don't get caught up in the details, just pay attention to the general ideas in the 'introduction' section and the way the lead was added in the 'materials and methods' section. I tried to highlight sections that would be most useful to you, but see what else you can find that might be of interest.

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For how you measure the response to lead... that could be your question: how do slugs respond to lead? You could measure appetite (total amount of food consumed compared to non-lead treated slugs) and movement (observe and count 'movements' for a consistent and specific amount of time, you'll have to define what you mean by movement, and how much time you will be counting the movements) and also compare them to your controls. You may also check for this book: Hopkin, S. P. (1989). Ecophysiology of Metals in Terrestrial Invertebrates. Elsevier, London, UK. It is available at the UCSB library.