Metals

1. Metals Fate and Effects

2. 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

3. Developmental and neurological effects of Hg on Japanese child, Minimata Bay, Japan

4. 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

5. 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

6. Change in Aluminum speciation as pH changes Note: most toxic form of aluminum is Al(OH)3

7. 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)

8. 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 ?

9. 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

10. 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

11. 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)

12. Effect of metals on body Na levels of the stonefly Acroneuria carolinensis from Grippo and Dunson, 1996

13. 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)

14. 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

15. 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)

16. 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)

17. 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