humus, definition of

Toxicity can be acute, subchronic, or chronic:

• Acute toxicity involves harmful effects in an organism through a single or short-term exposure.
• Subchronic toxicity is the ability of a toxic substance to cause effects for more than one year but less than the lifetime of the exposed organism.
• Chronic toxicity is the ability of a substance or mixture of substances to cause harmful effects over an extended period, usually upon repeated or continuous exposure, sometimes lasting for the entire life of the exposed organism.

• Peak soil
  "Dirt" (2008) by David Montgomery deals with the relation between soil erosion and civilization collapse. It is neither the first nor the only book that examines this subject. It is, however, written by a soil scientist, and it brings to a deeper level...