http://mars.jpl.nasa.gov/2001/lander/meca/

The Mars Environmental Compatibility Assessment (MECA) Project will characterize the Martian dust and soil, identify undesirable and harmful interactions with human explorers and associated hardware systems, and support the design of extravehicular activities and habitation systems.

Adhesion as the Agent of Hazards

For a particle to be hazardous to an astronaut, it must not only be intrinsically dangerous, but it must find its way into the astronaut's habitat, space suit, or vehicle. Adhesion is a way that particles can enter protected places: dirt can cling to the astronaut's spacesuit and be brought into the habitat where it can be inhaled or ingested, and where the toxic elements may become corrosive or poisonous.
If particles adhere to machinery, they can cause clogging of filters, seizing of bearings, and shorting of electronics. Astronauts attempting to remove the dust from solar panels and other sensitive surfaces can scratch those surfaces and decrease their effectiveness.

The following sections describe the different hazards that face astronauts and equipment on Mars due to adhesion.

Abrasion

Abrasion occurs when the Martian dust rubs against man-made surfaces. This can occur due to fast moving particles in the wind (sandblasting) or astronauts attempting to clean solar panels, windows, or lenses. If the dust particles are hard (like quartz), they will scratch the surfaces. If the dust particles are softer (like clay) then they may polish the surfaces and cold-weld moving parts together.
MECA will study abrasion by actively rubbing soil against test substrates under the microscope. Abrasion will also be seen in the MECA patch plates.

Corrosion

Corrosion is caused by chemical or electrochemical interactions of two or more materials. While corrosion due to two solids in contact with each other is not unknown, nearly all cases of corrosion are helped by the presence of a liquid.
When Martian chemicals are inadvertently transported into habitats, they will be activated by the addition of water. These salts, acids, or alkaline materials can then proceed to attack critical life-support components. Specific corrosion hazards for Mars explorers include corrosion of space-suit materials, airlock seals, and any equipment exposed for long durations as the compounds become activated by moisture in the air; and corrosion of human tissue when particles with a high or low pH settle on skin.

The understanding of the corrosion process dictates our choice of a soil/water mixture as the most direct measure of corrosion potential on Mars. Moisture-mediated corrosion will be studied in detail by the MECA wet chemistry laboratory.

Toxicity

Toxicity and pathogenicity refer to substances that cause illnesses and diseases, respectively. Breathable quartz particles are the most dangerous particles faced by industry on Earth. Pathfinder's apparent identification of quartz on Mars focuses the search on this material and other respirable particles.
Quartz will probably be the most hazardous substance, both for man and machinery, found on the Martian surface. In the respirable particle size range it causes silicosis and related diseases.

MECA will search for quartz particles by means of hardness tests on the microscope stage. Trace toxins will be measured by the wet chemistry laboratory.

Obstruction

Dust in the Martian atmosphere, lofted by a distant dust storm, presents no obvious hazard. It may, however, block sunlight for days or weeks and affect solar panel performance. A layer of dust will accumulate on the surroundings and on all the structures and equipment, leading to potential mechanical hazards.
The mechanical hazards may include:

Mechanical failure of space-suit joints due to clogging
Decrease in flexibility of woven materials as they become infiltrated with particles
Imparing of visibility through space-suit visors, habitat windows, and other transparent panels
Malfunction of filters and lenses on scientific test equipment
Reduction in efficiency of solar panels
Reduction in efficiency of heat dissipation or surfaces intended to absorb heat
Obscuration of panel labeling and warning signs, and
General surface degradation
MECA will measure mechanical capture of dust with filter samples on the microscope stage and with patches. It will also observe total atmospheric loading with the Robotic Arm Camera.

Electronic Failure

Electrical shorting of power lines or instruments due to electrical pathways made by dust is a common phenomenon in terrestrial arid or dusty regions. On Mars, arcing and shorting occur at far lower voltages than either on Earth or in open space due to the presence of a rarefied atmosphere. Conducting particles that accumulate on electrically active elements such as connectors and terminals could also induce shorting of electronic circuits. Even with precautions such as shielding, defects in coatings could result in shorting paths through conducting particle films.
Triboelectric charging due to frictional contact with dust and soil will be measured by MECA's electrometer. These phenomena are a direct result of adhesion, which will be studied in detail using the MECA microscopy station and patch tests.

Radiation Damage

When inhaled or ingested, some of the most dangerous particles are radioactive. Even a small amount of radioactive particles can cause an enormous amount of local tissue damage. Of the different types of radioactive sources on Mars, only airborne radioactive dust particles caused by scavenging of ionized radionuclides present a plausible hazard.
MECA will detect highly radioactive soil with its electrometer. Lower levels of radiation may be detected by the Lander radiation experiment.

Not to mention what any bacteria or viruses could cause...

Much more work needed with robots first.