Diatom Density
Definition
The number of frustules per unit volume of water in the drowning environment. Low-density environments (pools, tap water, diatom-poor rivers) cannot deliver a detectable systemic load even if drowning genuinely occurred.
- Measured as
- Frustules per unit volume of water
- Low-density environments
- Pools, tap water, diatom-poor rivers
- Effect of low density
- No detectable systemic load even in true drowning
Common questions
Why does diatom density undermine a negative diatom test result?+
A negative result in a low-diatom-density environment does not rule out drowning, because there may simply have been too few diatoms in the water to be aspirated and circulated in detectable numbers, so the test result has to be interpreted alongside the known diatom content of the recovery site.
How do investigators account for diatom density in casework?+
A comparison water sample is typically taken from the scene where drowning is suspected to have occurred, so the diatom species and approximate density found in the body can be checked against what is actually present in that water, rather than assuming a fixed baseline applies everywhere.
Related terms
- Background Contamination
- Diatom frustules introduced into a sample from sources other than the victim's own body: tap water, laboratory air, unclean glassware, reagents, and...
- False Negative
- A negative result from a preparation in which ante-mortem drowning actually did occur. Causes include low diatom density in the drowning water,...
- False Positive
- A test result that indicates the presence of a target analyte when it is absent. In forensic serology this may mean incorrectly...
- Positivity Threshold
- The minimum number of frustules per gram of tissue or per slide that a laboratory uses to declare a result positive. No...
- Standardisation
- The production of a validated, peer-reviewed protocol that specifies every variable in the test: acid type and concentration, digestion time and temperature,...