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Pathogen; pathogenic

Pathogens are infectious or toxin forming microorganisms causing disease. A food borne pathogen is a microorganism that causes illness through the ingestion of food.

Pentanes plus

A mixture of hydrocarbons, mostly pentanes and heavier fractions, extracted from natural gas. See hydrocarbons.

Per capita use

The average amount of water used per person during a standard time period, generally expressed in gallons per capita per day (gpcd). Per capita use can be calculated by dividing the total water use (including all uses such as for industry, commerce, residential, etc.) in an area by the population served but is most commonly calculated by dividing the residential water use by the population served.

Percolation

The movement of water downward and radially through subsurface soil layers, usually continuing downward to groundwater. The rate at which soils permit percolation is a measure of the vulnerability of groundwaters to contamination by surface waters as well as a determinant in the siting of septic fields.

Percolation, deep

In irrigation or farming practice, the amount of water that passes below the root zone of the crop or vegetation.

Perfluorocarbons (PFCs)

A group of human-made chemicals composed of carbon and fluorine only. These chemicals (predominantly CF4 and C2F6 ) were introduced as alternatives, along with hydrofluorocarbons, to the ozone depleting substances. In addition, PFCs are emitted as by-products of industrial processes and are also used in manufacturing. PFCs do not harm the stratospheric ozone layer, but they are powerful greenhouse gases

Permanent vegetative cover

Trees, or perennial grasses, legumes, or shrubs with an expected life span of at least 5 years. Permanent cover is required on cropland entered into the Conservation Reserve Program.

Persistent pesticides

Pesticides that do not readily break down in the environment. Becoming long-lived components of the ecosystem, these chemicals may have enduring effects at low concentrations or may bioaccumulate, posing hazards to higher predators.

Personal Saving

The difference between household income (after taxes) and consumption expenditures.

Pest

An animal or plant that is directly or indirectly detrimental to human interests, causing harm or reducing the quality and value of a harvestable crop or other resource. Weeds, termites, rats, and mildew are examples of pests.

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