Topic Area I-3 includes "non-point" source releases, pollutants that reach surface waters through sources other than discrete conveyances for effluents. This includes runoff from urban, industrial, agricultural, silvicultural or undisturbed land.

Cancer risks cannot be quantitatively assessed for this topic area. Insufficient exposure data are available to assess the cancer health risks from polycyclic aromatic hydrocarbons (PAHs), a class of indicator compounds that is predominantly attributable to non-point urban runoff. Cancer risk estimates calculated for both industrial and municipal point source releases also involve a component that can be attributed to non-point releases, because contaminated sediment in the aquatic environment serves as a continuous source of exposure to TCDD, DDT and PCBs for biota.

Two major sources of non-cancer risk are associated with non-point sources. First, leaking septic systems and other inadequate animal waste disposal systems (e.g., manure piles and feed lots) are a major source of microbiological agents contaminating surface water and occasionally causing outbreaks of gastroenteritis. (Most exposure to these agents occurs through non-point contamination of ground water by these same sources). Second, runoff from abandoned mines is the principal source of mercury contamination in edible aquatic organisms in California. Consumption of fish contaminated with mercury poses reproductive and neurological risks, particularly to pregnant women. Health advisories recommending reduced fish consumption apply to a number of lakes in California, as well as to the entire Bay/Delta estuary.

Relatively little is known about non-point source contributions to surface water and biotic contamination, although it is clear that such sources contribute substantially to ongoing exposures to persistent organohalides, trace elements and microbiological agents.

There are substantial data gaps in the information needed to describe the extent of aquatic resource contamination in California and the exposure potential of certain population groups at high risk (e.g., subsistence fishers), as well as to apportion responsibility between source categories. In spite of these limitations, overall confidence in the assigned rank is medium because opportunities for extensive human exposure to contaminants released into surface water are relatively limited. Drinking water exposures are generally unlikely, due to regulatory controls on the quality of water used in public drinking water systems. Edible organism exposure is limited by the relatively small proportion of the California population that fishes or hunts frequently, particularly in hotspot areas of known contamination which are posted with health advisories. Considerable uncertainties do surround our capacity to completely characterize the exposures of those who do regularly consume aquatic organisms. Monitoring efforts have historically been focused on a small subset of chemicals (about 25 "priority pollutants") discharged into aquatic environments. Available data are inadequate to characterize exposures to many of the substances found in urban and agricultural runoff. In addition, data on the size of population subgroups consuming edible organisms from different contaminated water bodies and on general population exposures are unavailable.

None identified.

Individuals relying on caught fish for a regular part of their diet are highly exposed to contaminated fish. Sport fisher people are more likely to be exposed than the general population. Individuals relying on surface water or wells for drinking water in rural areas with private septic systems may experience high exposures to pathogenic microbiological agents.

Risks to the general population are medium, because non-point sources are generally the major contributors to potential exposures to trace elements (from inactive mines), persistent organochlorines (from urban runoff in storm drains or contaminated sediment) microbiological contaminants (from leaking septic systems) and nitrates (from agricultural fertilizer use). There are limited opportunities for extensive human exposure to released contaminants through consumption of either drinking water or edible aquatic organisms. The most substantial risks involve exposure to mercury through fishing activities, but affected populations are small.

Groups that regularly consume large quantities of edible organisms from contaminated water segments are likely to experience significant health risks.