especially the ones with 7 tattoed on the bottom can leak components that mimic hormones, so-called endocrine disruptors.
without a liner may leak BPA/ Bisphenol A, especially from sour fruit or vegetables, like tomatoes, are also not a good idea.
How about using glass and ceramic and take a picnic basket. Less disposable stuff. If you do throw away glass, plastic, tin or paper and live in Jozi's Northern suburbs, contact our lovely neighbours, www.wholeearth.co.za for recycling.