There are reports of a drug on the PN causation lists which is also quite toxic to the bone marrow, showing up in shrimp that are farmed in Thailand and other countries.

http://www.cbsnews.com/2100-500262_162-644203.html

A longer article:
http://www.orionmagazine.org/index.p.../article/4395/

Chloramphenicol in honey from China:
http://www.hc-sc.gc.ca/dhp-mps/vet/f...enicol-eng.php

This drug is still available as Chloromycetin for rare, life threatening disease states, but was removed from sale in most countries otherwise in the 70's due to its toxicity.

Horse meat:
http://ec.europa.eu/food/food/chemic...untries_en.htm
This article details why horse meat may be dangerous, and it lists chloramphenicol and nitrofurans (this is Macrodantin/Macrobid a drug used in humans for bladder infections) may be present in the meat.
The article is pretty complex, but if you use the search function in Windows edit=find...you'll find the warnings.