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Metals. Fate and Effects. Overview. History of Metal Toxicity Oldest known toxin? (fall of Roman Empire due to Pb?) Water transported in lead pipes Wine enhanced by a grape-based syrup, cooked in lead-lined pots (250 ug/d. vs 45 ug/d. recommended by WHO) Minimata Bay, Japan

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metals

Metals

Fate and Effects

overview
Overview
  • History of Metal Toxicity
    • Oldest known toxin? (fall of Roman Empire due to Pb?)
      • Water transported in lead pipes
      • Wine enhanced by a grape-based syrup, cooked in lead-lined pots (250 ug/d. vs 45 ug/d. recommended by WHO)
    • Minimata Bay, Japan
      • Chisso Corporation dumped ~27 tons of Hg into bay starting in 1938
      • Mid-50’s  people began noticing symptoms of strange disease
        • Degeneration nervous systems, numbness in limbs and lips, slurred speech, constricted vision, serious brain damage, unconsciousness, involuntary movements, uncontrollable shouting.
        • Insane cats committing "suicide"
        • Sea birds dropping dead from the sky.
      • 1959  established that Hg had some how worked up through food chain into fish, people, animals
      • Chisso denied any wrong-doing, continued dumping Hg until 1968
overview con t
Overview (con’t)

B. Essential vs. non-essential metals

  • Essential metals - important as plant/animal micronutrients
    • Includes (Co, Cu, Cr, Fe, Mn, Ni, Mo, Se, Ti, Zn)
    • Over-enrichment can lead to toxicity
  • Non-essential metals
    • Always toxic above threshold level
    • Includes Pb, Cd, Hg
metal chemistry
Metal Chemistry
  • Metals are basic elements
    • Accumulates in organisms  not broken down by liver, etc.
    • Persistent in environment  last long time in sinks low/no exposure (no hazard) can come back out  hazardous again
  • pH effect (acidity = -log[H+])

Metal toxicity dependent on pH

1. Speciation- free ionic form usually most toxic  increase free iron as decrease pH

Note: exception to the rule  aluminum

metal chemistry7
Metal Chemistry
  • Metals are basic elements
    • Accumulates in organisms  not broken down by liver, etc.
    • Persistent in environment  last long time in sinks low/no exposure (no hazard) can come back out  hazardous again
  • pH effect (acidity = -log[H+])

Metal toxicity dependent on pH

1. Speciation- free ionic form usually most toxic  increase free iron as decrease pH

Note: exception to the rule  aluminum

C. Solubility/Precipitation

1. decreased solubility and increased precipitation as increase pH  both cause decreased toxicity

Summary – both chemical speciation and precipitation, and thus toxicity, is extremely dependent on pH (level of acidity)

sources sinks
Sources/Sinks
  • Sources – many different sources = many different metals entering the environment
  • Sinks
    • [polluted freshwater] > [polluted seawater]
    • High [coastal sediment] > high [freshwater sediment]

Conclusion – final sink is the ?

concentration ranges of selected trace metals
Concentration Ranges of Selected Trace Metals

Lower values in ranges are typical baseline concentrations; higher values are concentration reported at sites affected by human activities

toxicity
Toxicity
  • Ranges from slight reduction to rapid death
  • Very dependent on other environmental factors (especially water pH, hardness, and temperature)
  • Different mechanisms of toxicity depending on whether exposure is acute or chronic
acute toxicity
Acute toxicity
  • Most acute toxicity due to adsorption to gills (often little metal gets into animal, only body surface exposed)
  • Many metals cause body ion loss  ECF loss  circulatory collapse  death
  • Generally mollusks, fish more tolerant than other phyla  important to test several tropic levels for effect of any toxicant
  • In general  Cu > Hg > Zn > Pb to aquatic organisms
  • Results of acute toxicity test used to set allowable environmental limits (which will be chronic in nature) because hard to test metal effect over a long term  pH, hardness, etc change)
effect of metals on body na levels of the stonefly acroneuria carolinensis
Effect of metals on body Na levels of the stonefly Acroneuria carolinensis

from Grippo and Dunson, 1996

chronic toxicity
Chronic toxicity
  • Most often associated with assimilation into organism (high [metal] inside organism)
  • [chronic LOEC] <<< [acute LOEC]
  • Effects
    • Fish –
      • embryonic/larval most sensitive (spawning/hatching)
      • Teratogenesis
      • Growth reduction – due to reduced assimilation efficiency
    • Invertebrates –
      • each successive developmental stage more resistant than former stage
      • Period of larval settlement is crucial  any delay will increase mortality due to predation, disease and dispersion (wrong place at wrong time)
effect of metals on scope for growth

Metal contaminated sites

Effect of metals on scope-for- growth
  • Depressed scope-for-growth  theoretical instantaneous growth rate after ingestion, assimilation and respiration taken into account
    • Positive scope-for-growth = energy for growth, reproduction
    • Negative “ “ “ = animal is losing energy
regulation of metals
Regulation of metals
  • Water Quality Criteria (WQC)
    • Suggested maximum concentration suggested (set) by EPA
      • state sets standard = allowable limit of metal
    • Many metal standards based on hardness

Note: hardness may not have most effect on toxicity but effect is most well-known (most studied)

hardness based wqcs
Hardness-based WQCs
  • General formula

C = exp{a[ln(hardness)] + b}

where

exp = base of the natural log

a,b = constants determined by linear regression of ln(hardness) against the natural log of the median acutely lethal concentration (LC50)

C = allowable concentration (WQC)

examples of hardness calculated wqcs based on hardness value of 100 mg l hardness as caco 3
Examples of hardness calculated WQCs (based on hardness value of 100 mg/L hardness as CaCO3

Note: if hardness value entered in mg/L then calculated value will be in units of µg/L