What Are Necrosols and Why Are They Studied?

When you visit a cemetery, you probably think about your deceased loved ones, life’s daunting finiteness, and the place’s mournful solemnity and respectful silence. In other words, your reflections dwell in the non-material, metaphysical, and even spiritual realm.

However, for some people graveyards are of rather practical interest. These people are scientists who study cemetery soil. They even have a term for it: necrosol. And they believe their research has implications for ecology, forensic geology, and archaeology.

Necrosols as Anthropogenic Soils

Soil formation—or pedogenesis, as it is known scientifically—is governed by multiple factors, including underlying rock or mineral deposits known as parent material, climate, relief, vegetation, fauna, and time.

However, the development of civilization introduced another agent that researchers today have to reckon with. Soils modified by human activity are known as anthropogenic soils, or anthrosols.

The evolution of technology and industrialization resulted in another subtype: technogenic soils, or technosols. In different classification approaches, urban soils (urbanosols or urbisols) are either considered the same as technogenic soils, encompassing, among other things, mines and roads, or as soils specifically associated with cities.

In a city, soils can be modified by the addition of organic matter and artifacts, mechanical disturbance, or sealing them beneath pavement and other structures. Accordingly, scientists developed various qualifiers that help further classify urban soils, most notably urbic (in residential areas), ekranic (sealed), industric (in industrial zones), hortic (in parks and gardens), and garbic (in landfills).

In 1994, Wolfgang Burghardt, a German scientist, postulated the need for the “nekric” qualifier (nekros means “dead” in Greek) to describe a specific type of soils found at cemeteries and other burial sites. For soils with this qualifier, he used the term “necrosol” (Nekrosol in German), which was first proposed in 1986 by his compatriot Annerose Graf in her thesis on vegetation of West Berlin graveyards.

Thus, research on necrosols as a particular type of soil shaped by human activity at burial grounds, with specific morphological, chemical, physical, and biological properties, is relatively new.

Ladislav Smolík (1895–1960), a Czechoslovak soil and climate scientist, is considered the first to pay special attention to these soils in 1957, almost three decades before the term “necrosol” first appeared.

As recently as in 2004, Jaroslava Sobocká, a leading expert in the field from Slovakia, described necrosols as a “new” type of anthropogenic soils, which shows how young their study still is.

Nevertheless, we can look into what has been discovered so far.

Properties of Necrosols

The exact properties of necrosols predictably vary around the world depending on the original soil type, previous land use (for example, settlement or gardens), climate, and other factors influencing soil formation.

The age of a burial ground determines the amount of human remains and the stages of their decomposition, thus affecting the soil’s physical and chemical characteristics. Another factor is the area’s specific burial rituals and customs: inhumation versus cremation, coffins and other artifacts, embalming, and covering graves with stone slabs (which can alter the soil’s gas and water content).

However, scientists established some common properties of graveyard soils.

First of all, they divide these soils into burial (graves proper) and non-disturbed necrosols (spaces between graves and in the immediate proximity to cemeteries). The latter, while not being burial spots as such, may also contain chemical substances characteristic of necrosols, as well as traces of artifacts related to human visitations to the burial ground.

Researchers most often highlight the following properties of burial necrosols:

1. Mixed and disturbed soil horizons. This is mainly caused by grave digging and correlates with the depth of burial.

2. Presence of human remains and artifacts. The artifacts include coffins and their elements like nails, clothing, and everything else humans in different cultures put in graves (like pottery or weapons).

3. Increased amounts of phosphorus. This is not surprising since phosphorus has long been known to archaeologists as an indicator of human activity, including burials. Being one of the major elements released to the surrounding soil as a result of the decomposition of human remains (both soft tissues and bones), it is also the least susceptible to change and leaching, and so it remains in the soil for a long time.

4. Increased amounts of organic carbon, calcium, and nitrogen, as well as higher pH values.

Metal enrichment is also frequently mentioned, but it largely depends on other factors like the use of metal elements in coffins. The increase of aluminum, iron, lead, zinc, and rubidium was registered by researchers.

It should be noted that most studies deal with burials from the last few centuries. Longer timeframes may significantly modify the properties of necrosols.

Thus, a group of researchers who studied an ancient cemetery in Northern Poland related to the Wielbark culture—which is associated with the Goths and which flourished in the first centuries AD—discovered that, despite distinct morphology and physical properties, the cultural layer—the one of the burials proper—did not demonstrate increased concentrations of phosphorus, organic carbon, and nitrogen. They proposed to call this type of cultural layer “archaeo-necrosol.”

Practical Implications

But why is it important to study cemetery soils aside from purely theoretical interest? There are three major fields where the discoveries of these studies may be applied.

Ecology and Public Health

While industry, agriculture, and landfills are commonly viewed as major anthropogenic factors of environmental pollution, until recently cemeteries received little attention as potential contamination sources.

In 1998, the World Health Organization published a report titled “The Impact of Cemeteries on the Environment and Public Health,” which stipulated the need to assess the risks cemeteries pose to the environment and human health. This lead to more studies dealing with this matter.

A special attention was paid to the pollution of groundwater. It was noted that the proximity of cemeteries may cause groundwater pollution not necessarily because human corpses have any specific toxicity, but because they increase the concentration of organic and inorganic substances to levels that render groundwater unusable or undrinkable.

Examination of necrosols, their properties, and their impact on the environment may help determine which types of soils are more suitable for cemeteries, where they should be located in relation to human settlements, and which materials should be used for coffins, burial clothing, and embalming.

Some researchers focus on microbiological analysis of necrosols to determine risks to cemetery employees and visitors. They note that the primary risk is associated with injury and wound contamination during an employee’s performance of their work. Lesser risks include accidental inhalation, ingestion, or transfer of microorganisms to the mucous membranes of the eyes.

Another health-related risk is posed to archaeologists who work with burial sites that contain high concentration of toxic substances. In 1996, John L. Konefes and Michael K. McGee pointed out the potential danger of arsenic poisoning during archaeological excavations. In particular, arsenic was used as an embalming agent in the United States during the late nineteenth and early twentieth centuries.

Forensic Geology

Forensic geology, or forensic geoscience, is concerned with applying geological and wider environmental science methods and data to legal investigations.

The knowledge of the necrosol properties in a specific region may be used to discover clandestine burials. And while this approach is barely applicable to the search for individual graves of murder victims, it may be efficient in detecting mass burials like those associated with wars.

Archaeology

Similarly to forensic geology, necrosol studies may help archaeologists identify potential ancient burial sites.

Besides, some researchers point out that, while archaeologists focus on bone preservation, not enough attention is paid to burial soils. However, necrosols govern geochemical environment of bones and artifacts and may provide supplementary information to the study of skeletal remains and give some hints as to what could have disappeared with the passage of time.

Conclusion

As we have shown, the study of burial soils, known as necrosols, is a relatively new field within the wider soil science. Nevertheless, it has important implications and may help us improve our approaches to ecology and public health, investigate war crimes, and gain more knowledge about the past.