Older orchards are contaminated with lead arsenate from its use as a pesticide.

https://en.m.wikipedia.org/wiki/Lead_hydrogen_arsenate

Watering the groves from cheap pipes.

Neglect?

My money is on the cinnamon powder. Lead is kinda sweet, pretty common and quite heavy (and thus pretty cheaper per unit weight), and can make colorful pigments... if it wasn't for the toxicity, it could have made quite the versatile food additive. It wouldn't be the first time high levels of lead were found in dried spices/herbs; in fact, it's unsettlingly common.