Cadaver Islands and PMI Estimation

PMI intro

• Post-mortem Interval - estimation of time since death

• PMI is important to reconstruct events surrounding death

• facilitate solving crimes and identification

• Estimate PMI by examining changes in the body after death - decomposition and its interaction with the environment

• Decomposition causes microbial, fungal and chemical changes

• creating zones called cadaver islands 

• Provide valuable data for estimating how long a body has been dead

  

What is decomposition

• Breakdown of organic matter into simpler compounds through autolysis, putrefaction, and environmental interactions

• Observable and measurable changes over time

• Provide biological and ecological markers for PMI estimation

Decomposition stages

• Generally categorised into 5 stages due to their different physical and microbial changes:

  • Fresh: Cellular self-digestion and microbial growth begin

  • Bloat: Accumulation of gases causes visible swelling

  • Active decay: Rapid tissue breakdown, liquefaction, and strong odors emerge

  • Advanced decay: Decomposition slows as nutrients deplete.

  • Skeletal Remains: Soft tissues have decayed, leaving bones.

• Each stage can be identified by the physical and microbial changes

• PMI can be estimated based on decomposition progress

Cadaver island

• Nutrient-enriched soil zones formed beneath decomposing bodies

• undergo distinct physical, chemical, and biological changes throughout decomposition.

• Initial stages of decomp:

  • bodily fluids rich in nitrogen, phosphorus, potassium, and other organic compounds

  • seep into surrounding soil

  • change chemical composition 

• Active decay:

  • liquefaction of soft tissues 

  • release of decomposition gases

  • Impact soil pH and oxygen levels

• Advanced decay and skeletonisation:

  • remaining tissues decompose,

  • Enriching soil with nutrients

  • Form well-defined decomposition zones.

• changes impact the soil properties, microbial diversity and vegetation patterns.

• measurable, time-dependent changes that correlate with decomposition stages

• valuable indicators for PMI estimation.

Soil Chemistry Changes

• Chemical comp of cadaver islands change predictably:

  • Nitrogen, phosphorus, and potassium concentrations spike due to bodily fluids

  • Soil pH acidic due to decomposition fluids

  • Transitions to alkaline as decomposition progresses.

• Collect and analyse soil regularly

• Ion chromatography, mass spectrometry

• Measure nutrient concentrations and pH

• Quantify changes over time

• Match soil conditions with known decomposition timelines to estimate PMI

Microbial Activity

• Microbial communities in cadaver islands undergo predictable shifts over time

• Mesocosm experiments conducted to stimulate real burial conditions,

• Shows how decomposition impacts soil ecosystems over time

• Provides biological clock for decomposition

• Different bacterial and fungal species correlate with different stages

  • Initial: Common forest soil bacteria dominate: proteobacteria, acidobacteria, verrucomicrobia

  • Active decay: elevated carbon and nitrogen levels promote microbial activity:  Proteobacteria, Firmicutes

  • Advanced decay: anaerobic microbes, reduced oxygen availability:

  • Later stages: Microbial diversity increases, thriving in nutrient-rich environment - return of some taxa from initial soil communities

• DNA sequencing methods profile microbial and fungal communities

• Show stage of decomp - estimate PMI

  

Fungal Dynamics

• Fungi contribute to tissue degradation, nutrient cycling, environmental interactions

• Fungal species associated with decomposition

• Additional markers for PMI estimation

• Mycoforensics links fungal dynamics with decomposition stages

Organ Specific Investigations

• Microbiome in specific organs thanatomicrobiome undergo predictable changes after death

• There are organ specific patterns: unique microbial shifts

  • Circulatory system

  • Lungs

  • Gastrointestinal tract

• Profiling bacterial species in these organs and comparing them to known decomposition timelines

• PMI estimation

• Useful when external indicators are unreliable - severe environmental exposure, partial remains

Insect activity

• Cadaver islands attract insects

• Blowflies: Arrive shortly after death, laying eggs that develop into larvae and pupae at predictable rates.

• Beetles and scavengers

• Collect and analyse to determine species, developmental stages, colonisation patterns

• Forensic entomology links insect activity to decomp stages

• Estimate PMI based on life cycles and colonisation patterns

Impact on vegetation

• Decomp fluids and gases impact vegetation

• Early stages: toxic fluids kills flora, visible patches of dead vegetation

• Later stages: nutrient enrichment promotes regrowth and biodiversity.

• Changes in vegetation health and species composition

• time markers

• Remote sensing and imaging techniques

• Drone based imaging

• Detect patterns

• Useful for finding clandestine burials

• PMI estimation over large areas

Limitations - environmental variability

• Soil composition, temperature, moisture influence decomposition rates

• Arid environments slow decomp

• Complicates estimation

Limitations - Animal and Insect Activity

• Scavengers/burrowing animals disturb cadaver islands

• misleading changes

Limitations - Time frame limitations

• Most useful in early stages

• Reliability decreases over time

Limitations - complex soil interactions

Pre existing soil conditions obscure decomp related changes

Limitations - Ethical and legislative constraints

• Access to human remains limited

• Rely on animal substitutes - pigs

• Differences in physiology and decomposition dynamics pose challenges

• Comparative studies between animals and human remains to bridge this gap