Wilderness and Environmental Medicine. 8, 94-95 (1997)

ORIGINAL ARTICLE

Red snow: Is it safe to eat? A pilot studyDAVID C. FIORE, MD*, DENISE D. McKEE, MD, and MARK A. JANIGA, BS

Department of Family and Community Medicine, University of Nevada School of Medicine, Reno, NV 89557-0046, USA

The objective of this study was to detennine if the ingestion of snow contaminated with Chlamydomonas

nivalis causes diarrhea. The design was a single-blind crossover. Subjects were seven healthy volunteers, aged24-56 who ingested 500 g of snow contaminated with C. nivalis. Outcome was measured by stool and diarrheafrequency. No differences in stool or diarrhea frequency were noted between treatment and placebo groups.The conclusion is that in this pilot study, there was no evidence supporting the concern that ingestion of "redsnow" causes diarrhea.

Key Words: snow, algae, diarrhea, altitude

Introduction

Red or watermelon snow is a common phenomenon of thelate-season snowfields on the higher slopes of most moun­tain ranges in North America and throughout the world[l,2]. Although it had been described by Aristotle, and Dar­win observed the "bloody traces" that were left when walk­ing over certain snow fields [l}, it was not until the 19thcentury that plant (algal) material was found to be the causeof this red color [3]. Since that time, Chlamydomonas ni­valis has been identified as one of the primary snow algaeresponsible for this phenomenon, and much has beenlearned about the reproductive needs and capabilities of thisalga. Medical information on this snow alga, however, isstrikingly limited.

There are scattered reports that ingestion of red snow willcause illness, usually diarrhea, but confirmation of this be­lief is hard to establish. Unfortunately, it is so widely ac­cepted as fact that ingestion of red snow causes diarrhea thata respected guidebook states, "One should not eat pinksnow, since it is a pronounced laxative" [4].

The current pilot study was undertaken to determinewhether or not ingestion of red snow contaminated with C.nivalis causes diarrhea in human subjects under controlledconditions.

Methods

SNOW SPECIMENS

Snow with heavy red staining in an area identified previ­ously as heavily contaminated with C. nivalis was collected

* Address for correspondence: Department of Family and CommunityMedicine, University of Nevada School of Medicine, Brigham Building,MS 316. Reno, NV 89557-0046, USA.

J080-6032 © 1997 Chapman & HaJJ

on August 5, 1995, from the Mt. Rose Summit in Nevada(l9E-T17N-SWONWI/4) at an elevation of 2650-2750 m.The top 2 cm of snow was removed and discarded. The next5 cm of red snow was then collected and stored in sterilecontainers and transported immediately from the collectionsite to a storage freezer in Reno, NV. The snow was storedat approximately -3°C until the test data. Snow sampleswere allowed to melt partially, and then the snow wascrushed and blended with dark red Crystal Lite drink mix tomask any taste or color differences between the test andcontrol samples. Control samples consisted of crushed andblended ice mixed with the same Crystal Lite mix. Sampleswere measured into 500-g portions.

STUDY DESIGN

The study consisted of a single-blind crossover, with a one­month washout period. Subjects recorded a stool log for 8days after the date of sample ingestion. Subjects were alsocontacted 2 weeks after ingestion to confirm results of thestool log and to assess whether or not there was late devel­opment of gastrointestinal complaints. The study was ap­proved by the University of Nevada Human Subjects Re­view Committee.

SUBJECTS

Subjects were seven healthy volunteers between the ages of24 and 56.

STATISTICS

Within-subject analysis was performed using paired I-testsand repeated-measures MANOVA utilizing SPSS 6.0 soft­ware (SPSS Inc., Chicago, IL).

Red snow: Safe to eat?

Results

Seven subjects ingested both red snow and control samplesand completed the stool logs. One subject completed onlythe control phase and was excluded from analysis. Stoolepisodes for the two groups (red snow and control) wereidentical, 7.14 stools per subject for each 8-day period (SDred snow 2.9, SD control 2.0). Diarrheal episodes were alsoid~ntical, with two diarrheal stools in each test period.PaIred t-tests making within-subject comparisons betweenred snow vs placebo for stool frequency and diarrhea fre­quency revealed no significant differences. Repeated­measure MANOVA examining variables by day within sub­jects also revealed no significant test effect.

Discussion

The current study suggests that ingestion of red snow in the~ake ~ahoe Basin does not cause diarrhea within 8 days ofIllgestlOn. Study subjects were contacted 2 weeks aftercompletion of the study to determine if there had been any~ate consequences. No subject reported a significant changeIII stool frequency or consistency. The one subject who didreport one day with two loose stools after ingesting the redsnow was a physician in a student health clinic and felt thatshe had contracted the intestinal flu that was prevalent oncampus at that time.

There are a few limitations of the current study. First wasthe small sample size. However, there was no trend detectedin the current study, even when MANOVA analysis wasperformed looking for variation within subjects by day. Sec­?nd, ~~e i~gested snow samples were not analyzed for algalIdentIfIcatIOn or degree of contamination. However, previ­ous work had identified these snowfields as heavily con­taminated with C. nivalis and had failed to locate other snowalgae. This finding is consistent with other work in theSierra Nevada Mountains [5]. Snow samples were obtainedfrom the top 7 cm of snow, after removing the very top 2 cmto limit contamination. Previous work has demonstrated thatsnow algal concentration is greatest near the surface [1].Third, the snow samples were not ingested immediatelyafter collection but were transported and kept frozen untilthe study was performed approximately I month later. Bo­tanical studies have demonstrated that C. nivalis can survivefreezing for periods of longer than 7 years and remainhealthy [6]. It is possible that different life stages of C.nivalis may be responsible for the lack of diarrhea in thisstudy. We tried to reproduce field conditions by letting the

95

frozen snow sample partially melt. Because C. nivalis can­not reproduce in temperatures above approximately 4°C, itis very unlikely that it would be invasive in humans. Fur­thermore, it is not recognized that any blue-green alga pro­duces toxins, is invasive, causes diarrhea in humans by anyother mechanisms (Ron Hoham, personal communication).

If C. nivalis does not cause diarrhea, why does wildernessfolklore report that ingesting red snow will cause it, andwhy do we continue to read anecdotal reports of such illeffects [5,4,7]? One proposal, put forth by Thomas, is thatthe snow is often very dirty, and factors other than the algaemay be responsible for the diarrhea [5]. In the current study,a concerted effort was made to remove the top, dirty layerof snow before collecting specimens. We also think it ispossible that red snow is suffering from recall bias. Theincidence of diarrhea after any kind of travel (includingcamping) is higher than at home. If one had ingested redsnow while hiking or camping, the red snow seems a likely,although perhaps innocent, suspect.

Although the results of this pilot study suggest that in­gestion of red snow, contaminated with C. nivalis, does notcause diarrhea, we do not recommend that mountaineersingest red snow with abandon. The results of this studysuggest that ingestion of moderate quantities of red snow inthe Sierra Nevada range will not cause diarrhea, but thisstudy does not address the ingestion of larger quantities oringestion of red snow from other regions. A larger study orstudies from different areas may be indicated to confirm thesafety of eating red snow.

References

1. Tiffany, L.H. Algae: The Grass oj Many Waters. Springfield,IL: Charles C Thomas, 1900: 97-102.

2. ~errath, J.F., Nicholls, K.H. A red snow in Ontario cause bydmofiagellate, Gymnodinium pascheri. Can J Bot 1974; 52683-685. '

3. Hoham, R.W. Optimum temperatures and temperature rangesfor growth of snow algae. Arctic Alpine Res 1975B; 7, 13-24.

4. Whitney, S. A Sierra Club Naturalist's Guide: The Sierra Ne­vada. San Francisco, CA: Sierra Club Books, 1979.

5. Thomas, W.H. Observations on snow algae in California. JPhycol 1972; 8, 1-9.

6. Harris, E.H. The Chlamydomonas Sourcebook: A Comprehen­sive Guide to Biology and Laboratory Use. New York: Aca­demic Press, 1989: 22-130.

7. Hallagan, L.p., Interlandi, S. Don't eat that watermelon snow.Wild Med Lett 1996; 13,9-14.