zeolite An ion exchange resin material.

zeta potential In coagulation and flocculation procedures, the difference in the electrical charge between the dense layer of ions surrounding the particle and the charge of the bilk of the suspended field surrounding this particle. The zeta potential is usually measured in millivolts.

Z-list OSHA's tables of toxic and hazardous air contaminants.

zonation The distinct, conspicuous layers (or belts) found in soils, vegetation, bodies of water, and on mountains.

zone of aeration The comparatively dry soil or rock located between the ground surface and the top of the water table.

zone of saturation The soil or rock located below the top of the groundwater table. By definition, the zone of saturation is saturated with water. Also, see water table.

zooglea A jelly-like coating developed by bacteria.

zoogleal matrix The floc or slime formed by zoogleal bacteria. Also called zoogleal film.

zoonoses An infectious disease that is transmissible under normal conditions from animals to humans.

zoonotic disease or infection An infection or infectious disease that may be transmitted from vertebrate animals (such as a rodent) to humans.

zooplankton Small, usually microscopic animals (such as protozoans), found in lakes and reservoirs.

Zulu time (Z) One of seve ral names for the twenty-four hour time that is used throughout the scientific and military communities. Other names for this time measurement are Universal Time Coordinate (UTC) or Greenwich Mean Time (GMT). See Greenwich Mean Time for more information.