Step 1: Meaning of cleanliness in spice/herb powders.
- The term "cleanliness" primarily refers to freedom from extraneous matter such as dirt, sand, and soil contamination.
- A direct measure of this is **acid-insoluble ash**, which indicates the inorganic matter (like silica, sand, dirt) not soluble in acid.
Step 2: Evaluate each option.
- (A) Acid-insoluble ash → measures extraneous dirt/contamination → directly indicates cleanliness.
- (B) Pesticide residue levels → safety-related, but not immediate cleanliness.
- (C) Volatile oil content → indicates quality/flavor, not cleanliness.
- (D) Mycotoxin levels → relates to fungal contamination, important for safety but not basic cleanliness.
Step 3: Conclude.
The very first test for cleanliness of spice/herb powders is acid-insoluble ash content.
Final Answer:
\[
\boxed{\text{(A) Acid-insoluble ash content}}
\]