The spanish version of the article[1] links to the alternative explanation (Bayer Nemacur pesticide):

[1] https://es.wikipedia.org/wiki/Enfermedad_del_aceite_tóxico_d...

[2] http://www.cbgnetwork.org/129.html

[3] http://cbgnetwork.org/1522.html

As early as 1981 relevant spanish newspapers were telling the same story:

[4] http://free-news.org/index02-pag.htm

[5] http://free-news.org/cambio01.htm

Edit:

This is the last interview to Dr. Muro:

[6] http://free-news.org/afaber02.htm