Sunday, February 1, 2015

Sifting Through the Sediments: Parasite Eggs from Night Soil Contexts

While the last thing that most people would want to get in the mail is night soil, I'm one of those people who excitedly awaits for jars of this stuff to arrive. (Because one: Such material is super cool and because two: "most people" are boring.) In my last two posts, I discussed how we look for parasites in the context of mummified tissues and desiccated feces. Today, I'm going to introduce you to another great source of literal pay-dirt for archaeoparasitologists.

Night Soil Sediments from the Past
A nightman's calling card from the 1800s.
For those who haven't been introduced to the phrase "night soil", I'm referring to dirt that has human fecal components. The term originated from the olden days when people would shovel human waste out of cesspools and outhouses during the night and later usually sell the excrement to farmers as a fertilizer. Many of these people employed as "nightmen" or "night soil men" were not allowed to work during the day and made up a portion of the lowest of low classes in most places. This was early human waste management in Europe, Africa, and Asia long before modern standards of disposal.

As you've probably already figured out, there were lots of problems with sanitation in the past. Before modern indoor plumbing, people found a variety of ways to store their steaming piles of...stuff...before nightmen could come and haul it away. Some were indoor chambers for relieving oneself. This included things like chamber pots or water closets (the early ancestor to modern flushing toilets). Others were outdoor pit latrines such as the outhouse, the privy, the dunny, the biffy, or the long-drop.

As excrement, other waste materials, and soil fill these types of features, evidence of parasites is preserved in a stratigraphic way (with the oldest layers at the bottom and the youngest layers at the top). Archaeologist excavate these types of features along with middens (trash heaps), cisterns, and other collections of human waste from sites all over the world. These sediments are collected with provenience information carefully recorded and dates associated with other things recovered from the same layer.

Analyzing Latrine Sediments
Once these sediments make their way to people like me, they are examined using a sequential analysis model (or at least they should be) to gather all of the information that can possibly come from such material. To process this type of material, first we treat sediments with hydrochloric acid to react with any microfossil-binding calcium carbonate that might be present. Next, we use distilled water to screen heavy sediments and separate macrofossils (big pieces of plants, minerals, bones, insect remains, etc.) from microfossils (parasite eggs, starch granules, pollen, etc.) using the swirl technique. The macrofossils are dried and examined via a stereoscopic microscope. The microfossils are examined via light microscopy and exposed to further processing as needed.

SEM of Lycopodium spores.
Depending on the nature of the samples, we may need to use dangerous chemicals like hydrofluoric acid (for dissolving silicates) or zinc bromide (for heavy density flotation). We are very careful when using such things as they can be harmful if precautions aren't taken to protect ourselves. For example, we wear eye protection all the time...especially when we use zinc bromide because it attacks the optic nerve if splashed in your eye and can blind you. We also have lots of special safety protocols when we work with hydrofluoric acid as it can stop your heart if enough gets on your skin and you aren't treated quickly. Rule #1: Never do it alone, just in case. I'll be using this acid later this week for some sediments from Iowa. There will be two other people in the lab...one working on mites, and one hanging around in case I have any problems.

We also treat sediments with Lycopodium spore tablets just like we treat coprolites and mummy intestines. By adding a known amount of these spores as markers, we are able to quantify our microfossils and make sense of their presence in our samples. We use a microfossil concentration formula to determine the number of microfossils per unit (weight or volume) of sediment.

Taphonomic Issues
Like other kinds of archaeological materials, we must always consider the state of preservation for our samples. The addition of chemicals to break down excrement is something to be aware of in samples from certain places and time periods. As I learned from a recent set of historic samples from Missouri, the microfossils found in cisterns are fewer in number and much more degraded than those found in privies from the same time period.

We also must consider how often the sediments were exposed to abiotic agents of change, like wind and water. A series of wetting and drying episodes can degrade things as hardy as sporopollenin-laden pine tree pollen grains over time, leaving no evidence of anything that was once there. Biotic agents, like coprophagus (poop-eating) fungi, bacteria, and animals, can also affect what we find in latrine sediments.

From Privies to Parasites
Without going into too much detail about the types of microfossils found in latrine sediments, I thought I'd let all of you parasitophiles see some of the groovy parasite eggs that have been found from these contexts.

Parasite eggs recovered
from cemetery sediments.

Unfertilized  egg of
Ascaris lumbricoides


Molecular techniques have also been used on sediments to search for evidence of parasites that don't leave visible traces of themselves. Enzyme-linked immunosorbent assays (ELISAs) have been applied to samples in order to detect a number of protozoan parasites such as Giardia sp., and Entamoeba histolytica. 

Example ELISA plate.
Yellow wells = positive samples.
The Moral of the Story
Like mummies and coprolites, sifting through latrine sediments elicits reactions of both disgust and amazement from those following your work. The data that can be gathered from such studies are immense in volume and intensity. I have conducted a number of contract archaeology jobs that involved the analysis of latrine sediments, so I can literally call these types of material "pay-dirt" from both a scientific and from an economic standpoint. It is sad that so few researchers understand the importance and potential of examining latrine sediments, but at the same time this allows those of us who do see the value in these studies to work without a lot of interference. As always, these kinds of studies provide the best means of understanding what past people were eating and what exactly were eating them.

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