coating CCA posts with tar to prevent arsenic leeching?

Question

Is that even an option?

Answer 1

Unless your harvesting crops next to the posts, I don't see the need. You'd just be covering one bad chemical, Arsenic, with many more unknown chemicals in tar. If your using them to make a raised bed, you can drape the poles on the inside of the bed with plastic before you fill it with soil. Same applies to railroad ties and creosote. RScott

Answer 2

Options for Treated Lumber, Plywood, Wood Preservatives, and Fence Posts
Before selecting which alternative products to use, the producer needs to evaluate each situation for:

Effectiveness of the product for the task and conditions.
Durability of the product and the life expectancy required for the task.
Availability of the product.
Ease of installation.
Cost effectiveness of the product and any maintenance needed
Safety.
An expensive option but with complete safety
Redwood, Cedar wood or the new composite wood made from recycled materials.

http://attra.ncat.org/attra-pub/lumber.html#options