Someone recently mentioned this in a thread, only the brand was spelled "Ziplock." I did a search on the word but apparently the search function only looks at OPs. However, since then I saw a reference to these bags being BPA-free. I followed up and here's what I found:

"BPA Free
SC Johnson’s Ziploc® brand Bags and Containers are BPA free. Our products are extensively evaluated for toxicity and safety and comply with applicable quality and safety regulations. A recent study conducted and published by the University of Cincinnati found that the estrogen-like chemical bisphenol A (BPA) has been shown to encourage the growth of a specific category of prostate cancer cells. BPA is commonly used in the manufacture of certain plastic products such as food-can coatings, milk-container liners, food containers, and water-supply pipes. Many reports of this study note that this chemical is commonly found in plastic food storage containers.

Dioxin Free

A few years back, concerns were raised about the alleged dangers of using plastics in microwaves. The presumption argued that a combination of fat, high heat and plastic releases dioxin into food and ultimately into the cells of the body, which would then increase the risk of producing cancerous cells. After we researched these claims, it became clear that the information was misleading and unnecessarily alarming. Dioxins only form when chlorine is combined with extremely high temperatures (such as 1,500 degrees F). The most powerful kitchen microwave oven will never reach this temperature. Even if you reached 1500F (theoretically), all Ziploc® brand products are 100% dioxin-free.

FDA Requirements

When label directions are followed, Ziploc® brand products can be used with confidence. All Ziploc® brand Containers and microwavable Ziploc® brand Bags meet the safety requirements of the U.S. Food and Drug Administration (FDA) for temperatures associated with defrosting and reheating food in microwave ovens, as well as room, refrigerator and freezer temperatures."