Half-Life
The period of time necessary for one half of a substance
introduced to a living system or ecosystem to be eliminated
or disintegrated by natural processes. Hazardous Air Pollutants
HAPs
Any air pollutant listed as such in Title III of the
1990 Clean Air Act Amendments. These are chemicals that
have the potential to cause serious health effects. HAPs are released by mobile
sources and industrial sources. Also referred to as air toxics.
Related Programs - Clean Air Act Hazardous
Waste
A waste which, because of its quantity, concentration, or characteristics,
may be hazardous to human health or the environment when improperly treated, stored,
transported, or disposed. Specific definitions of hazardous waste vary by statute
or regulation. Heavy Metals
Metallic elements with relatively high atomic weights that can contaminate groundwater
and surface waters, wildlife, and food. Heavy metals
have the potential to be toxic at relatively low concentrations. Examples include
arsenic, cadmium, chromium, copper, lead, mercury, selenium,
and zinc. Hexachlorobenzene HCB
A critical
pollutant once used as a pesticide for grain protection until banned by the
U.S. in 1976. It is still produced as a byproduct during the manufacture of other
chlorinated hydrocarbons. It is a persistent
toxic substance and is found in the tissues of fish, animals, and humans from
the Great Lakes Basin. Limited uses of HCB are still permitted.
Related Programs - Binational Program
House Great Lakes Task Force
A bipartisan coalition of U.S. Representatives
from Great Lakes States that works to advance the economic
and environmental health of the Great Lakes region. Human
Health Criteria
These are descriptive or numeric expressions that
specify how much of a pollutant can be allowed in a water body and still allow
for the protection of human health. See also water quality
criteria. Related Programs - Great Lakes Initiative
Hydric Soils
Soils that are saturated, flooded,
or ponded long enough during the growing season to develop anoxic
conditions in the upper part of the soil profile. Hydrocarbons
A class of compounds that contain hydrogen and carbon. This group
of compounds includes the naturally occurring hydrocarbons produced by plankton,
as well as many petroleum-based products like gasoline and motor oil. Chlorinated
hydrocarbons, a subclass of hydrocarbons, are human derived and generally toxic.
Hydrophytic Vegetation
Plant life capable of growing
in wet conditions, such as in water or in soil or other substrate that is periodically
saturated with water. The presence of hydrophytic plants is one of the indicators
used in wetland identification and delineation. Related
Programs - Wetlands Conservation Act, Wetlands
Conservation Act Rules. | 
