TOWARD ESTABLISHING LEVELS OF CLEANLINESS

The problem of how to penetrate kilometers of the ice sheet and sample subglacial aquatic environments in the cleanest and least intrusive manner possible remains a con-siderable technological challenge. Current drilling technologies are not sterile; drilling fluids may contain both microbes and substrates for microbial growth. In addition, the

0 EXPLORATION OF ANTARCTIC SUBGLACIAL AQUATIC ENVIRONMENTS

ice sheet itself contains living microbes, and the extreme climate makes it impossible to carry out drilling without introducing microbes from humans.

The inadvertent introduction of microbes that might grow in these waters is of highest concern. Not only will living microbes potentially alter the aquatic systems, but also exogenous DNA³ will interfere with research using molecular technology.

Accordingly, it is of critical importance to minimize the introduction of exogenous microbes,⁴ and even exogenous nucleic acids,⁵ to allow for proper investigation of the

“true” microbial community (and not contaminants) and prevent changes in microbial communities through the introduction of growth substrates or toxic materials to the subglacial aquatic environment.

Drilling and sampling apparatuses may also add water-soluble oils used in metal working during the fabrication of the instruments and equipment, as well as phthalate ester additives that are used extensively in the plastics industry. The impact of minute quantities of oils and additives may be small and much reduced if they are rapidly diluted by mixing processes in the subglacial environment. Localized effects are pos-sible, however, if mixing is slow; if the mixing volume is small relative to the quantities added; or if the contaminant does not dilute in water (e.g., nonaqueous-phase liquids).

It is likely that contamination of subglacial aquatic environments during drilling, sam-pling, and monitoring cannot be eliminated, only minimized.

Given that some contamination with microbes is inevitable, what level is accept-able? The only known quantity is the number of microbes present in the deep glacial ice. Using this quantity as a baseline, the committee suggests that fluids, drilling, or sampling equipment introduced into the subglacial aquatic environment should not contain more microbes than are present in an equivalent volume of deep glacial ice.

From the available evidence, this amount is expected to be a few hundred cells peris expected to be a few hundred cells per milliliter. This level of contamination should be considered a provisional rule; when new data become available on microbial populations in these subglacial environments, the standard should be changed to reflect this new information.

Research activities targeting one component of the environment may potentially contaminate or alter another component. For example, sampling may disturb the internal stratification of the lake and change its physical and chemical structure. Sedi-ment sampling may transfer biota from sediSedi-ments and near-bottom waters to overlying water and ice, which may compromise subsequent measurements of the upper waters and ice. Sediments are likely to contain orders-of-magnitude higher concentrations of microbes, nutrients, and metals than are present in the water column. These benthic microbial communities also are likely to be different from those in the water column.

In addition to assessing potential impacts of research activities prior to their start, the committee recognizes the importance of initially sampling sites furthest downstream within a subglacial drainage system to reduce the impact of any contaminants intro-duced into the drainage system and the importance of maintaining records of materials introduced into the environment to inform future investigations.

Cleanliness requirements for the exploration of subglacial aquatic environments include (1) cleaning hardware (and quantifying microbial levels) prior to penetration, (2) maintaining hardware cleanliness during penetration, and (3) designing research

3DNA that originates outside an organism.

4Microbes that are introduced to closed biological systems from the external world.

5Nucleic acids that originates outside an organism.

FINDINGS AND RECOMMENDATIONS

techniques that minimize the possibility for cell transfer between different levels in the ice and the lake bed itself. If an environment has unique biological systems, transfer may also occur as a robotic sampling device moves between different environments.

Thus, it will be important to minimize the level of microbial contaminants on drilling, sampling, and monitoring equipment to ensure that these activities have a minor and/or transitory impact on the environment.

Although there is no definition of minor or transitory in the Antarctic Treaty, in practice, Antarctic Treaty parties have considered the chemical impacts on the Ant-arctic environment; these considerations may provide a context in which to evaluate potential microbial impacts. The primary concerns surrounding addition of chemicals to the environment have been to determine the contaminant level that can be detected, how long it would continue to be detectable, and what effect the total amount might have on the system. This has been of particular concern for example, in assessing the impact of chemical species in coastal sewage outlets. In practice, if the chemical is not detected, due to dilution, within a short distance from the end of the pipe, then the effect of the contaminant on the environment has been considered as less than minor and transitory. With this definition of minor and or transitory in mind, the committee considers the addition of contaminants which do not change the measurable chemi-cal and/or biologichemi-cal properties in a volume equivalent to the borehole as a less than minor impact. Based on these considerations, the committee offers the following recommendations:

Recommendation 7

Drilling in conjunction with sampling procedures will ineitably introduce micro-organisms into subglacial aquatic enironments. The numbers of microbial cells contained in or on the olume of any material or instruments added to or placed in these enironments should not exceed that of the basal ice being passed through.

Based on research to date, a minimum of 0 cells / mL^– should not be exceeded, until more data are aailable.

Recommendation 8

Drilling in conjunction with sampling procedures will ineitably introduce non-liing chemical contaminants into lakes and associated subglacial aquatic eni-ronments. Toxic and biodegradable materials should be aoided, as should the introduction of nonmiscible substances. At a minimum, the concentrations of chemical contaminants should be documented and the total amount added to these aquatic enironments should not be expected to change the measurable chemical properties of the enironment. The amount added would be expected to hae a minor and/or transitory impact on the enironment.

Recommendation 9

Notwithstanding their compliance with Recommendations and , inestigators should continue to make eery effort practicable to maintain the integrity of lake chemical and physical structure during exploration and sampling of water and sediments.

EXPLORATION OF ANTARCTIC SUBGLACIAL AQUATIC ENVIRONMENTS