The ingredient you worry about is creosote. When active it exudes a tar-like substance and odor. Plant something close to the ties and see how it grows. If it is stunted, yellowed or dies, the ties are too active. You can line the beds between the ties and the growing area with a heavy plastic until the action of the preservative dies down. It is best not to get the "tar" on your skin. Yes, it does weather out and most RR ties that are sold are indeed fairly well detoxified. I actually have RR ties that are very old and I was sure all was OK when weeds started to grow well next to and in them.

Railroad ties (and telephone poles) are no longer allowed by law to be used in landscaping. Railroad ties contain creosote and pentachlorophenol. Creosote is a black mixture of coal tar chemicals that can be taken up by plants. Pentachlorophenol is a wood preservative used until 1987. Both are classified as a probable carcinogenic. More information can be found at: National Pesticide Information Center - Treated Wood.

It is unknown, as research is limited, how much either of these chemicals can leach into the soil and therefore, how much is up taken by plants. Testing your soil for heavy metals can be done, although testing for these exact chemicals is not known and would most likely be quite costly. This publication from the Oregon Health Authority, Heavy Metals in Soil - Analytical Laboratories Servicing Oregon, has information on labs that test for heavy metals. Be sure to check with them before sending them a soil sample.

To reduce your risk, start by removing the railroad ties and the surrounding soil. For new raised beds, use materials that have not been treated with chemicals. Some longer lasting wood choices are cedar or redwood and think about non-wood choices such as concreate blocks or rocks. Consider using landscape cloth before bringing in new, fresh soil, this will prevent roots from new plants from entering the possibly contaminated soil below. There are fruits and vegetables that are better to grow in this situation. Tomatoes, corn, cucumbers, and many berries are good choices. Avoid green leafy and roots vegetables. Soil Contaminates and Best Practices for Healthy Gardens, is an excellent publication that will give you more ideas on how to approach possible soil contamination from railroad ties and other causes.

Amanda, follow the advice from Jan Gano. My beds are from before the legal proscription and are pretty much decayed by now. We are replacing with masonry block beds mostly. My apologies for not double checking.
Thank you,