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Section 13: Surface Water Pathway - Human Food Chain Threat

The Human Food Chain threat is distinctive in two ways. The focus is not on whether the water of the sediments are contaminated, but on whether there is evidence that the contamination has penetrated through the biological food chain to the aquatic organisms that humans consume.

  • Humans are the targets. Aquatic organisms that humans consume are the route of exposure.
  • An observed release may not be sufficient to define actual contamination. Further evidence is required that shows the impact of the likelihood of release on the aquatic organisms that human beings eat.

Bioaccumulation is assessed for this threat and for the environmental threat.

  • The maximum value for waste characteristics is 1,000 rather than 100. This means that high threat scores can be obtained with relatively few target points.
  • The value assigned to Food Chain Individual frequently drives the score for this threat. Where there is bioaccumulation, the subsistence fisherman whose principal protein source is locally-caught fish can be at very high risk.

The Human Food Chain Threat score is subject to a maximum of 100. This threat score is added to the threat scores for the other two surface water pathway threats to get the pathway score.

13.1 Waste Characteristics

Waste characteristics is the product of toxicity, persistence and bioaccumulation potential factor values.

  • The bioaccumulation potential factor value (BPFV) indicates the tendency of certain substances to accumulate in the fatty tissue of aquatic organisms and to be found there at concentration orders of magnitude greater than the concentrations in the surface water and the sediments.
  • HRS rule, page 51617, Section, describes how the (BPFV) are calculated.
  • SCDM provides two values for bioaccumulation for the human food chain threat (fresh water and salt water) and two values for the environmental threat. The values for the human food chain threat are based on data from aquatic organisms that human beings eat. The values for the environmental threat are based on data for all aquatic organisms.
  • HRS rule, page 51617 describes the procedure for choosing between the fresh water value and the salt water value.
  • Section 8.3, pages 239-240, of the HRS Guidance Manual gives definitions of fresh water, salt water, and brackish water. It also discusses how to apply these definitions in the selection of a bioaccumulation factor value.

The algorithm for calculating waste characteristics is a bit more complex, because the BPFV is now included in the selection of the most hazardous substances, along with toxicity and persistence.

Waste Characteristics Concluded(2)

The first part of the algorithm is already familiar: toxicity times persistence times quantity, capped at 108. The BPFV is then used and the product is capped at 1012. The maximum score for waste characteristics from HRS Table 2-7 is now 1,000.

13.2 Documenting the Presence of a Fishery

Two items of documentation are required for a fishery:

  • An aquatic human food chain organism is present in the surface water body.
  • Some attempt has been made to catch the human food chain organisms for human consumption.

Aquatic human food chain organisms are organisms that human beings eat. Do not confuse this HRS definition with the broader concept of the biological food chain that includes all organisms, beginning with the microscopic.

  • More than fish are included. Consider shellfish, crustaceans, amphibians, and amphibious reptiles.
  • Note that birds such as ducks and mammals such as moose are not included as aquatic human food chain organisms.
  • If aquatic organisms that are not generally eaten can be documented to be consumed locally, provide the documentation and consider them to be aquatic human food chain organisms.
  • If a fishery is now devoid of human food chain organisms because of contamination attributable to the site you are assessing, count that fishery as though it still existed. This is a general HRS principle: where a resource such as a well or a fishery has been lost because of contamination attributable to the site, count that resource in the HRS evaluation. See Section Q of the Preamble to the Revised HRS, page 51567 and also the Preamble to the final original NPL at 47 FR 40664, September 8, 1983.

Fishing is defined as an attempt to remove aquatic human food chain organisms for consumption.

  • Fish and game personnel, rural sheriffs, tackle stores, and other local people can often identify where people fish.
  • Supporting documentation has included paths made to fishing locations, wrappings for lures, or filament caught in trees.
  • If a fishery has been closed or is "catch and release," provide documentation that people nevertheless take fish home for consumption.

13.3 Targets

Targets are the food chain individual and the population. Both are assessed for Level I, Level II, and potential. Note the parallel treatment in other pathways and threats (HRS rule, Table 4-1, page 51608).

  • Population is assessed by converting the pounds of fish production for each fishery into people-equivalents, based on generic assumptions about fish consumption.

The surface water in-water segment must be divided into fisheries.

  • Break the in-water segment into fisheries that are exposed to Level I, Level II, and potential contamination.
  • Further segment fisheries exposed to potential contamination by surface water body types (dilution ranges from HRS Table 4-13, page 51613).
  • Further segment fisheries where the species harvested change or where there is a major change in production (poundage) per acre. These changes are particularly likely when you move from one surface water category (river, lake, etc., from HRS Section 4.0.1, page 51605) to another or move from shallow to deeper water.
  • Note that there may be two or more fisheries within the same zone of contamination or within the same dilution regime.

13.4 Actual Contamination

In documenting actual contamination, evidence is needed that not only have hazardous substances entered the water or sediments (observed release criteria), but that these substances have moved through the biological food chain to the organisms that humans consume.

There are three criteria that can establish actual contamination of the human food chain. Please read carefully HRS rule page 51620.

The first criterion is the most commonly used and is the simplest: show that there has been an observed release of a hazardous substance with a BPFV of 500 or greater.

  • The inference behind this criterion is that substances with rather high bioaccumulation potential are the ones that are most likely to have penetrated through the biological food chain and be found in the tissue of organisms that humans eat.
  • Substances with high bioaccumulation factor values include many polyaromatic hydrocarbons (PAHs), most pesticides, and metals such as cadmium, copper, mercury, radium, selenium, and zinc.
    • Bioaccumulative substances tend to sorb and are more apt to be found in sediment samples than aqueous samples.

Actual contamination is also assessed when a fishery has been closed because of the presence of a specified hazardous substance and that this same substance is found in a observed release from the site.

  • The inference behind this criterion is that the closure of the fishery was in response to a health threat due to the presence of the substance and that the presence of that same substance in the observed release documents that the site has contributed to the health threat.

The third criterion is the most definitive of actual contamination but the least used: document an observed release by a sample from an essentially sessile, benthic, human food chain organism.

  • Especially in fresh water, the essentially sessile, benthic organisms may not be locally consumed.
  • It is difficult to detect many substances in a biological matrix unless they contain chlorine or metals.

The sampling point(s) that document actual contamination of the human food chain are used to establish a zone of actual contamination that extends from the most downstream (or farthest) sample back to the PPE.

There are two ways to determine Level I; both involve tissue samples because the benchmarks are stated in terms of milligrams per kilogram of edible tissue.

  • When preparing tissue samples for shipment, select only the edible portions. If fishermen cook the fish skin down, send the fillet and attached skin as most representative of risk. If further portions of the organism are consumed, document that fact and send those edible portions. Fatty portions and livers are apt to show high bioaccumulations.

Level I concentration can be established when an observed release is documented by a sample from an essentially sessile, benthic, human food chain organism.

  • The "essentially sessile, benthic" establishes that the organism stays put so that background and release levels can be compared.
  • The "human food chain organism" establishes that the observed release substances have impacted organisms that human beings eat.
  • If substances that meet the observed release criteria also meet or exceed a human food chain benchmark individually or in the aggregate (the I or the J index), Level I concentrations are established.

Level I concentrations can also be established by a fish tissue sample, and other non-sessile, benthic organisms, providing all three criteria of HRS rule, page 51620 are met.

  • Non-sessile, benthic organisms like fish move around and cannot, in themselves, be used to establish an observed release or a zone of actual contamination.
  • Within the zone of actual contamination established by other samples (aqueous, sediment, tissue) a "territorial" aquatic organism is caught, and a substance found in the organism's tissue was also found in the documentation of the zone of actual contamination, the HRS assumes that the load of contamination found within the organism reflects, at least in part, the impact of contamination attributable to the site. The contamination level in the organism is compared against benchmarks and may establish Level I concentrations (HRS Guidance Manual, Highlight 8-48 : Samples and Criteria for Level I and Level II Concentrations in the Human Chain Threat, page 299).
    • The HRS Guidance Manual, Highlight 8-47 : Use of Tissue Samples from Aquatic Organisms, page 297 gives examples of aquatic organisms that are apt to spend extended periods of time within the boundaries of actual food chain contamination.
    • The location where the organism was caught can document a zone of Level I concentrations if all the criteria are met.

Zones of Level I, Level II, and potential contamination for the human food chain threat are established, based on the sampling points discussed above, in the same manner that zones are established for the drinking water threat.

13.5 Food Chain Individual

This factor will frequently drive the score for the human food chain threat.

  • Example: An observed release of an unknown quantity of PCBs is documented by samples in a freshwater wetland. Turtles are trapped in that area of the wetland for turtle soup. Score the human food chain threat. Look up the values for PCBs in SCDM.
    • HRS Guidance Manual, Highlight 8-50, page 301 provides generic values assigned to targets.
    • In this example, the score is 96.00. The likelihood of release is 550, based on an observed release to the wetland.
    • Waste Characteristics is 320. The values for PCB are 10,000 for toxicity, 1 for persistence (lake), and 50,000 for BPFV (fresh). The minimum value for quantity is 100, because a fishery and a wetland are subject to actual contamination.
    • Targets is 45, the value for food chain individual at Level II. PCBs, with a BPFV of 50,000 can establish actual contamination but only a tissue sample can establish Level I.

Documenting a Level I or II fishery may be particularly tricky when the zone of actual contamination is small. How do you document that anyone ever fishes within this specific zone? If you cannot document fishing within the area, can it be called a fishery?

Review HRS rule, page 51620, all of Section This provision is critical when you have a sediment sample or an outfall with a high BPFV substance (500 or greater) and cannot document that the zone of actual contamination is fished.

13.6 Food Chain Population

HRS Table 4-18, page 51621 performs the cross-walk between pounds of edible tissue and the people-equivalents of this poundage. This table assumes a BPFV of 1, because bioaccumulation is considered in waste characteristics not targets.

Determine the poundage of edible tissue produced from each fishery within the target distance limit. Use HRS Table 4018, page 51621, to find the population value associated with each fishery.

Multiply the population value for each fishery at Level I and Level II by the appropriate multipliers. Enter the products on HRS Table 4-1, page 51608 (HRS Guidance Manual, Highlight 8-50 : Comparison of Scoring Level I, Level II, and Potential Contamination, page 301 for these multipliers).

For all of the fisheries at potential contamination, apply the HRS formula on page 51621 of the HRS rule.

  • Note that the summation operator is applied to each fishery, not to each dilution range. If there are two or more fisheries within the same dilution range, treat each fishery individually. This approach differs from the drinking water and environmental threats.
  • Do not forget to apply the 1/10 for potential to the sum of the dilution-weighted population values for the potential fisheries. Enter the results on HRS Table 4-1 as the value for potential human food chain contamination.

13.7 Estimating Fishery Production

The HRS Guidance Manual Section 8.13, pages 305 through 316, provides many helpful tips regarding sources of information and methods of documenting the production of fisheries. The following are some basic principles.

  • Fairly good catch information is more likely available in the more heavily fished areas. In other areas, catch may be light and production values low.
  • Convert all data into an estimate of the poundage of edible tissue. This is particularly important with data on the total tonnage of shellfish.
  • You are estimating the poundage associated with a specific reach of a water body. If you have data from a larger area you will have to apportion the poundage, usually on the basis of surface area.
  • Beware of landing data for a port. It doesn't usually document where the fish were caught.
  • Make your best estimate of production and check it against HRS Table 4-18. It may not make sense to try to refine the estimate, because you'll still be in the same production category or, because the resulting number will be trivial after dilution weighting is taken into account.

Look particularly for productive or well-stocked fisheries that are subject to actual contamination.

For potential contamination, look for productive fisheries in low-flow regimes where dilution-weighting won't lower the population value to insignificance. Lakes with small inflows and oxbow lakes are examples. Note the usual dilemma: large water bodies that have large production are usually heavily dilution-weighted. Small water bodies with a dilution weight of 1 frequently have minimal production.

The HRS Guidance Manual suggests that you use "back-of-the-envelope" production values and check the impact on score to see whether the effort of getting good-quality data is worthwhile.

If data are lacking, or if the gathering of data is found to be "not efficient" (the HRS Guidance Manual term), you can resort to the default documentation of "production unknown but shown to be greater than 0 by the presence of a fishery" and assign a population value of 0.03 from HRS Table 4-18, page 51621.

13.8 Questions and Answers

Which substance will give the higher score for waste characeristics and why?

The second gives the higher score (1,000), because no value is lost to the cap of 108. The first substance loses two orders of magnitude to the cap and gives a score of 320. This happens only when hazardous waste quantity is at its maximum value of 1,000,000.

Turtles are trapped for soup in the wetland. Is this a fishery?

Yes.    The wetland is an HRS surface water body, the turtles are an aquatic human food chain organism, and they are removed for human consumption.

What value would you assign for food chain individual if you have an area of actual contamination on a small to moderate stream and cannot document that anyone ever fishes there? The area might, for instance, be very small, on private property, fenced, or relatively inaccessible compared to other nearby fishing locations. You can, however, document that the river a mile downstream is a fishery and that people fish within the mouth of the stream.

20. Based on the third bullet. If it were not for this bullet, you would have to consider the mouth of the stream the nearest fishery and multiply by 20 for potential, times a dilution weight of 0.1 for a small to moderate stream.

Scenario A: Production is 40 pounds per acre per year, a nice value for a stocked fishery. The river is about 40 feet wide and has a stream flow of 200 cfs. The fishery is 15 miles long and is exposed to potential contamination. What is the value for potential population? (Note that 40 feet x 15 miles x 5280 feet/mile / 43,560 ft2 per acre = about 73 acres.)

0.003. Annual production is about 2920 pounds (73 x40) and gives a population value of 3 from HRS Table 4-18, page 51621. The dilution weight from HRS Table 4-13, page 51613 is 0.01.

  • 3 (population) x 0.01 (dilution) x 1/10 (potential) = 0.003
  • Note in this exercise that the pounds per acre of annual production can vary in a rather large range before it makes any difference in the resulting value for potential population.

Scenario B: What is the potential population value if the fishery is a minimal perennial stream with a production that is either unknown or less than 100 pounds?

  • 0.003. Annual production is "greater than 0 to 100 pounds" and gives a population value of 0.03 from HRS Table 4-18, page 51621.
  • The dilution weight from HRS Table 4-13, page 51613 is 1.
  • 0.03 (population) x 1 (dilution) x 1/10 (potential) = 0.003

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