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Advisory Committee Meeting #3 September 16, 2008 North San Francisco Bay Selenium TMDL Draft Numeric Target PowerPoint Presentation
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Advisory Committee Meeting #3 September 16, 2008 North San Francisco Bay Selenium TMDL Draft Numeric Target. Barbara Baginska San Francisco Bay Regional Water Quality Control Board. Presentation Overview. Background: Numeric targets in TMDL context Problem in North SFB

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Presentation Transcript

Advisory CommitteeMeeting #3September 16, 2008North San Francisco BaySelenium TMDLDraft Numeric Target

Barbara Baginska

San Francisco Bay

Regional Water Quality Control Board

presentation overview
Presentation Overview
  • Background:
    • Numeric targets in TMDL context
    • Problem in North SFB
    • Exposure types and bioaccumulation
  • Target Development
    • Species at risk in North SFB
    • Toxicity thresholds for local ducks and fish (exposure levels, local data, mitigating conditions)
  • Fish tissue-based target: why and how?
  • Proposed target and rationale
numeric target definition
Numeric Target - Definition

Numeric targets are specific goals for TMDLs that ensure protection of designated beneficial uses of waters and provide basis for data analysis and allocations

numeric target selection
Numeric Target - Selection
  • A numeric target can be:
    • numeric water quality objective
    • numeric interpretation of narrative objective; or
    • numeric measure of some other parameter necessary to meet water quality standards
  • Usually expressed as specific water column, sediment and/or tissue indicator
  • Will demonstrate attainment of water quality standards
  • Easy to monitor
water quality criteria
Water Quality Criteria
  • San Francisco Bay and Delta

Freshwater numeric criteria apply:

    • Acute-Criterion Maximum Concentration : 20 µg Se/L
    • Chronic-Criterion Continuous Concentration : 5 µg Se/L
  • California

Saltwater numeric criteria:

    • Acute -Criterion Maximum Concentration : 290 µg Se/L
    • Chronic-Criterion Continuous Concentration : 71 µg Se/L

Selenium does NOT exceed the CTR chronic criteria

of 5 µg/L in North SFB

problem to solve
Problem to Solve
  • 303(d) listing:
    • Affected use is one branch of the food chain most sensitive indicator is hatchability in nesting diving birds
    • exotic species may have made food chain more susceptible to accumulation of selenium
    • health consumption advisory in effect for scaup and scoter (diving ducks)
  • Se concentrations in benthic invertebrate, fish, and bird tissue collected from the Bay have been measured at concentrations known to cause reproductive and toxicological effects in some species
harmful versus beneficial
Harmful versus Beneficial

Adapted from NRC 2005

where does se come from
Where Does Se Come From?
  • Volcanic deposits
  • Mining (copper, phosphate, coal)
  • Oil production and refining
  • By-product of coal burning power plants
  • Food (plant foods, grains, cereals and nuts)

National Institutes of Health 2004

water versus dietary exposure
Water versus Dietary Exposure
  • Water column Se has marginal impact on toxicity to higher level aquatic organisms
  • Observed selenium toxicity in fish results predominantly from dietary intake
  • Type of diet contributes to exposure and vulnerability
    • Filter-feeding benthic organisms ingest and assimilate particulate selenium to high concentrations
    • Bioaccumulation by invertebrates (zooplankton and bivalves) is critical to fish and birds
not all food webs are equal

It’s better to be a shrimp!

Not All Food Webs Are Equal

Terri Reeder, Selenium Game , San Diego 2005

target development approach
Target Development Approach
  • Review of fish and avian selenium toxicity
    • 80 fish toxicity studies (1987 -2007)
    • 46 avian toxicity studies
  • Identify species of concern in North SFB
  • Establish species-specific toxicity thresholds
  • Consider mitigating factors (diet, length of exposure, sulfate content, loss rates)
  • Compare with known effect levels
toxicity thresholds in birds
Toxicity Thresholds in Birds
  • No direct toxicity information for birds in North SFB
  • Most data for chickens and mallards
  • Sensitive endpoint: -reproductive success
    • egg hatchability
    • egg fertility
    • chick survival
diving ducks exposure in nsfb
Diving Ducks Exposure in NSFB
  • Feeding pattern - benthic mollusks, shellfish, crustaceans
  • Clams in scoter diet (SB = 100%, SPB = 25%)
  • Spend winter in SFB
  • Breed in Alaska and Canada
  • Rapid elimination rates – background levels after 70 days
  • New data: Se in eggs of scoters from NSFB below levels of concern for sensitive species
  • No reproductive effects for muscle tissue concentrations (2.1 – 5.7µg/g-ww, Lemly 1998)
white sturgeon
White Sturgeon
  • Identified as likely the most affected species in NSFB
    • Feeding pattern - benthic organisms
    • Clam eater (77% of stomach volume)
    • Present year-round in NSFB
    • Reproductive biology may contribute to bioaccumulation
    • Highly variable bioaccumulation rates
    • Toxicity data available
    • Tissue concentrations exceed known thresholds

After W. Beckon, pers. com

sacramento splittail
Sacramento Splittail
  • Potentially affected fish in North SFB
    • Feeding patterns - benthic organisms
    • Clam eater (34% of stomach volume)
    • Spawns in the upper Estuary
    • Can cope with high-level short-term exposure
    • Rapid elimination rates
    • Tissue concentrations below known thresholds and indicative of background level diet
fish tissue target why how
Fish-Tissue Target – Why & How?
  • 2004 EPA draft aquatic life criteria – fish tissue
  • Fish considered to be the most sensitive to chronic selenium exposure
  • Accounts for protection of wildlife from the harmful effects of selenium
  • Expressed as whole-body tissue concentration on a dry weight basis
    • Offers direct link to chronic endpoints and
    • Integrates many site-specific factors (chemical speciation, rates of transformation, temporal variations)
    • Easy to sample
numeric target derivation
Numeric Target Derivation
  • Toxicity thresholds
  • For sensitive environments numeric target should be more protective than EC10
  • Geometric mean of boundary concentrations
numeric target rationale
Numeric Target Rationale

Fish-tissue – 6 µg/g whole body dry weight

  • Proposed numeric target:
    • Established for species most at risk in North SFB and based on local data
      • Waterfowl depurates Se quickly after leaving the Bay
      • Se concentrations in bird eggs at background levels
      • Clam-eating bottom feeders - white sturgeon - most at risk
    • Within range of known thresholds protective of aquatic wildlife
    • Conservative and considers mitigating conditions in North SFB
    • Protective of human health (fish consumption)
human health
Human Health
  • Fish Contaminant Goal (OEHHA 2008)

Tissue Concentration (ppb) =

[(RfD * Body Weight)–BDL]/CR = 7.4 ppm ww (29.6 ppm dw)

  • Allowable duck tissue consumption
    • Original health advisory still in place
    • Scaup and scoter tissue concentrations < 6ppm ww
screening of available studies
Screening of Available Studies
  • NOAEL and/or LOAEL reported
  • chronic exposure tested
  • selenium exposure was the only treatment
  • tissue data reported
  • laboratory experiments under controlled conditions
  • dietary exposure scenario used
how our numeric target compares with known thresholds
How our Numeric Target Compares with Known Thresholds?

a – Compiled from Presser and Luoma, 2006 (Table 13, 14 and 15)

b – Lemly (1998) (Table 1), values represent measured concentrations showing whether adverse effects are likely to occur

c – Values in parenthesis indicate concentrations typical for uncontaminated aquatic systems