Pollutant Chemicals and Toxicity:

Transcription

1 Lecture 18 Pollutant Chemicals and Toxicity - examples from Heavy Metal Contaminants in fresh water Please read Chap. 6, 19 ( just ) and 22 (just ) of your text (chapters 7, 20 and 23 in the 9 th ed.) Today: 1. general aspects of environmental toxicology 2. heavy metal toxicity and sources to the environment Next time: 3. heavy metal contaminants in some fresh water and near shore sea waters. Pollutant Chemicals and Toxicity: simple classification of pollutants a) Organic b) Inorganic c) radioactive d) Biological (which we will not discuss in this class). Table 6.1 of Manahan further categorizes pollutants based upon their chemistry and effect in the environment. Notes: Trace metals, radionuclides and P and N nutrients are all "inorganic" pollutants, but each behaves differently in the environment and can therefore be classified separately. The distinction between "organic" and "inorganic" breaks down for some heavy metals that are bound in organo-metallic compounds (e.g., dimethyl mercury, tributyl tin). 1

2 Pollutant Chemicals and Toxicity: Other simple classifications of pollutants a) Liquid b) Solid c) Gas/vapor d) aqueous Steps for dealing with contaminant discoveries: 1. determine net detrimental effect (i.e., definition of a pollutant. "Detrimental effects" almost always involve harmful situations to organisms. Not all pollutants are detrimental at all concentrations. an ecologist ascertains the net negative, positive or neutral effects of that substance on various organisms within that ecosystem to assess impacts. Next, look at fate and transport For verified or suspected pollutants: 2. how do contaminants become distributed in the environment? 3. Examine how long the pollutant is expected to persist in the environment from: source fluxes natural dispersion/attenuation chemical and microbial reactivity 2

3 Finally, look at impacts on target populations and remediation methods: 4. What organisms come in contact with the polutant, at what concentration level and at what frequency. Related: how toxic is the material? 5. Devise methods to remediate the problem based on what was learned in steps 1 to 4. Toxic chemical Intake pathway: Organisms come in contact with toxic substances in 3 main ways: 1. Ingestion 2. Inhalation 3. Dermal Contact The Pollutant may interact differently with an organism over each of these pathways. Toxicity levels differ for specific chemicals as well. 3

4 Toxicity Risk Assessment Conceptual Site Model This example was developed to consider pathways to human receptors from a heavy metal contaminated soil. Some Biological Factors Involving Heavy Metals in the environment: Essential Metal - Required by an organism at some level; turns toxic at some higher concentration. Non-Essential Metal - Not required by an organism at any level; turns toxic at some higher concentration. 4

5 Some Biological Factors Involving Heavy Metals in the environment: (These terms and definitions also apply to other contaminant types as well) Food Chain Factors: Plants and animals vary widely in their ability to regulate metal content. Additionally, metals (as well as other things such as some halogenated hydrocarbons) can not be broken down or excreted by many organisms. Instead, they remain in the body of an organism and increase in concentration throughout it's life. Just like other chemicals in the environment, we can categorize pollutants as conservative (not changing with respect to other constituents and non-conservative (changing ) Some Biological Factors Involving Heavy Metals in the environment: (These terms and definitions also apply to other contaminant types as well) Food Chain Factors: Pollutants such as heavy metals can enter the environment in any number of ways. Then, geosphere-biosphere hydrosphere-biosphere atmosphere-biosphere exchanges, plus within-ecosystem exchanges all contribute to subsequent distribution into organisms, including those we use for fod.. 5

6 Some Biological Factors Involving Heavy Metals in the environment: (These terms and definitions also apply to other contaminant types as well) Food Chain Factors: Badly conflated on internet Bioaccumulation - conservative pollutant buildup in an organism over its life. Biomagnification - the increase in concentration of a conservative pollutant up the food chain approaches/persistence-and-bioaccumulation-of-persistent-organic-pollutants-pops- Time 1 Time 2 This nice figure from is bioaccumulation, not biomagnification as labeled Food Chain Factors: 6

7 Differentiation of metals in various parts of organisms: Hg (above) (below) 7

8 Reversibility - Uptake is reversible for this organism. Other Effects - PbNO 3 acts as a nutrient to this diatom (siliceous shell bearing phytoplankton) because Pb has a low toxity to this organism and the added NO 3- acts in the standard nutrient fashion. Toxicity assessment determined from the dose-response relationship, wherein the percentage of individuals in a population showing a particular response is plotted as a function of "dosage" of a toxicant. LD = "lethal dose", which is the typical toxic effect most environmental scientists use for maximum allowable concentration in the environment. 8

9 Toxicity factors of specific chemicals Sub-lethal effects are those that harm but don't kill an organism. They usually occur at lower concentrations Relationships between exposure, doses, and effects Depending upon the situation, policy makers and environmental scientists may use the dosage for a sublethal effect as the maximum instead (typically the case when human exposure is involved). 9

10 Table Salt (ingested) 10 6 The toxicity on a gram per gram basis is quite variable from substance to substance Polonium 210: estimated at 10-5 if inhaled) to 5 x 10-5 (if ingested) Some specific toxic effects of metals on various organisms: Cu or Zn 10

11 biological activity of toxic metals Heavy metals inhibit enzymes (by binding) and protein synthesis They cross membranes by passive diffusion/pinocytosis The target /critical organ for most metals is the kidney (Victor, 2014) Example - Influence of some heavy metals on aquatic vertebrates. MT = metallothionein: small cysteine-rich protein thought to play a critical role in cellular detoxification of inorganic species by sequestering metal ions that are present in elevated concentrations. From Wang et al., 2014, Characteristics, functions, and applications of metallothionein in aquatic vertebrates, Front. Mar. Sci.,

12 Factors related to the overall toxicity of the chemical elements includes alkali metals, alkaline earths, halogens and a few others. Calling them noncritical is not to say that toxic compounds of these elements do not exist; rather, these are the least problematic in general Includes elements that are more toxic, and more/less accessible in common polluted environments. Notice that more toxic metals tend to be in the center of the periodic chart (moderate electronegativity). In general it is many of these metals' ability to make covalent or partially covalent bonds with natural Lewis bases found in organisms (O, N and S bearing molecules) that allow them to disrupt biochemical functions and result in adverse effects. Ironically, Lewis acid behavior of some of these metals also can make them essential nutrients at other times (e.g., Co, as in B vitamins). Other general characteristics that contribute to metal toxicity (Victor, 2014) 12

13 Chemical, physical and biological factors that influence metal toxicity. Age factor example: Inorganic lead salts enter the body ingestion or inhalation. For adults only about 10% of the does ingested by an adult is absorbed, where as up to 50% might be absorbed by children. Condition of organism example: More Pb is absorbed lead if a person is deficient in Fe, Ca or Zn. Heavy Metal Pollutant Sources and Cycles. aqueous speciation, and sources of a few of the most problematic toxic metals. Concentrated deposits of one metal or another within the near-surface rocks of a watershed (e.g., ores) occasionally erode naturally to produce toxic concentrations in the hydrosphere. However, disruption of these ore bodies by mining is what usually accelerates their rate of introduction into the environment. 13

14 Heavy Metal Pollutant Sources and Cycles. (Victor, 2014) Heavy Metal Pollutant Sources and Cycles Except in extreme point source contamination cases pollutant concentration in a given location typically depends on geochemical cycling over multiple input sources and pathways, with inter-reservoir exchange. Not all aspects of the complete box model in Fig. 1 may be required to understand pollutant distribution in a given area, but the better our overall understanding of the movement of a pollutant through the environment is, the better equipped we are to deal with problems. 14

15 Heavy Metal Pollutant Sources and Cycles aquatic environments (Victor, 2014) Heavy Metal Pollutant Sources and Cycles Notice for example that the atmosphere is a significant source of metals deposition to the North Sea, although rivers and dredging are also major players for these 4 metals. 15

16 Heavy Metal Pollutant Sources and Cycles Globally, something like 50% of the atmospheric content of many metals is from natural sources such as volcanoes, forest fires and windblown dust. Heavy Metal Pollutant Sources and Cycles Atmospheric deposition is not constant around the globe. These open ocean values reflect input variations, atmospheric circulation patterns and variable rainout rates. 16

17 The common industrial use(s) of a number of metals, the rate of recycling within those industries and some alternatives (some also problematic). Long term improvements in metals pollution will require improved industrial activities or alternative materials 17