A Preliminary Assessment of Ecological Risks from Nonylphenol in Municipal Sewage Sludge Following W

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A Preliminary Assessment of Ecological Risks from
Nonylphenol in Municipal Sewage Sludge Following
Wastewater Treatment

• Charles Staples, Ellen Mihaich, Carter Naylor,
  Brent Huntsman
• Aquatic Toxicity Workshop
• Winnipeg, Manitoba, Canada
• October, 2001

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Background...

• Nonylphenol ethoxylates (NPE) are widely used
  surfactants in North America
• Cleaners and detergents
• Industrial processing
• Spent NPE in wastewater sent to sewage treatment
  plants (STP)
• Well functioning treatment plants can remove gt95
  of all NPE and its biodegradation intermediates

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Background...

• STP effluents
• NPE1,2 and NPEC1,2 (carboxylated NPE)
• traces of NP and other degradation intermediates
• STP sludge
• NP is the major metabolite found
• Landfilled / incinerated / applied to land
• Potential environmental risks from residues
• Effluent discharges recent CEPA assessment
  report
• Sewage sludge applied to land this assessment

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Objectives...

• 1. Examine the potential environmental risks from
  sludge applied to soil
• microbes, plants, invertebrates, small
  mammals
• potential for groundwater contamination
• 2. Use the results of the preliminary risk
  assessment to suggest additional data to usefully
  improve the assessment

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Basic approach follows EPA (1998) guidance on
Ecological Risk Assessment...

• 1. Problem Formulation Phase
• Establish assessment goals
• Develop conceptual model
• 2. Analysis Phase
• Calculate exposure concentrations
• Develop no effect levels

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EPA (1998) guidance on Ecological Risk
Assessment...

• 3. Risk Characterization Phase
• Quantitative assessment of exposure and
  effects data
• Uncertainty analyses

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Problem Formulation Phase - Conceptual Model

• Sludge gt Soil
• Soil gt Direct contact with soil organisms
• Soil gt Ingestion by small mammals
• Soil gt Migration to groundwater

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Analysis Phase - Exposure Concentrations...

• Sludge applied to soil
• 500 ?g/g dry weight NP (including other NPEs)
• 8 t/ha per 5 years maximum allowed
• assumed 4 t/ha applied twice during the 5-y
  period
• Sludge mixed with soil to a depth of 15 cm
• 1 ha of soil 15 cm deep weighs 2000 t
• Net dilution is 500X, so Csoil is 1 ?g/g, dw

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Analysis Phase - Major pathways deemed complete...

• Sludge to field to
• contact with soil microorganisms / activity
• contact with plant roots
• ingestion by insects
• ingestion/contact by earthworms
• accumulation in earthworms and plants to small
  mammals

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Analysis Phase - Exposure Concentrations...
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Analysis Phase Critical Toxicity Values...
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Risk Characterization - Hazard Quotients (need
to be lt1.0)...
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Risk Characterization Phase - Uncertainty
Analysis, main issues...

• Considered only most exposed receptors
• Used toxicity data that found no effects at any
  test concentration
• Used toxicity data based on NP added to soil
• Sludge application rates
• Ignored biodegradation in sludge-amended soil

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Biodegradation of NP in sludge-amended soil...
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Conclusions...

• NP/NPE in sewage sludge applied to soil is not
  expected to result in adverse impacts
• Groundwater is not expected to be impacted from
  sludge applied to soil
• NP in sludge is much less available to pose
  toxicity than NP directly applied to soil
• basis, Krogh et al. (Denmark) applied 21 t/ha
  NP-containing sludge to fields and found it was
  non-toxic
• reasons avoidance / biodegradation /
  availability

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Refinements to this preliminary analysis...

• Uptake of NP / NPE in plants
• Translocation of NP / NPE within plant tissues
• Quantification of NP/NPE concentrations in sludge
  from a diversity of locations
• Incorporation of biodegradation into the exposure
  calculation
• Microbes and plant toxicity data conducted using
  NP mixed into sludge, then amended into soil