Botulism risk with refrigerated items

AFAIK, you are not in significant danger of botulism in any kind of pickling or brining, refrigerated or room-temperature. The acid and/or the salt prevents the growth of botulism bacteria. Garlic oil is a specific danger because it has neither acid nor salt, and canned tomatoes because they don't have enough acid (yes, really).

That's not to say that you couldn't get other unpleasant microorganisms, but not botulism.

I am not a biologist or doctor, though. Hopefully we'll hear from one.

Botulism thrives in high-moisture, low-acidity, low-salinity, anaerobic environments at between 50 and 130 degrees.

In your refridgerator pickles, you're:

1. keeping cold
2. adding acid
3. adding salt

All of which should at least prevent the botulism from reproducing in great enough numbers to be toxic, if not outright killing it.

That's not to say nothing nasty can grow in refrigerator pickles — you're likely safe from botulism, however.

You won't grow significant cultures of clostridium botulinum in temperatures below 50°F. On the flipside, unfortunately, refrigerator temperatures - while retarding growth - do not destroy the bacterium or inactivate or destroy its toxin.

The good news is, normal boiling inactivates present toxins, so even if you have c. botulinum present in the brine but boil it, the combination of both the inactivation of the toxin and the retardation of growth in low temperatures makes brining a pretty safe activity.

Furthermore, c. botulinum really dislikes high acid environments. Brines are usually rather acidic. It's important to note that it takes 250°F over three minutes to cause significant damage to clostridium botulinum. All other means, such as boiling at sea level pressure or refrigerating/freezing only slows culture growth and prevents the production of botulinum toxin. That means even if you cooked, boiled, and froze your food, leaving it out in the danger zone for too long still poses a risk. Obviously pressure-canning does significantly lower it.