INTERACTION BETWEEN ELEMENTS AND TERRESTRIALMARINE SYSTEM Chemical Interactions

INTERACTION BETWEEN ELEMENTS AND TERRESTRIAL/MARINE SYSTEM

Chemical Interactions It is rare that organisms in the environment are exposed to a single toxicant. Typically, multiple toxicants are present, and can interact in a variety of ways.

The United States Environmental Protection Agency has one of the more detailed and precise definitions of toxic interaction, designed to facilitate risk assessment. [15] In their guidance documents, the no-interaction default assumption is dose addition, so synergy means a mixture response that exceeds that predicted from dose addition. The EPA emphasizes that synergy does not always make a mixture dangerous, nor does antagonism always make the mixture safe; each depends on the predicted risk under dose addition.

Classification of Chemical Interactions: 1. Additive: 2. Synergistic: 3. Potentiation: 4. Antagonism:

1. Additive: Combined effect of chemicals is equal to the sum of each chemical's effect alone (4+4=8). AKA, Independent Joint Action Most commonly observed effect is additive egs. , combinations of chemicals in same class (organophosphate insecticides, PAHs, narcotics).

2. Synergistic: Combined effect of chemicals is greater than the sum of each chemical's effect alone (4+4=20). AKA, Super additive egs. carbon tetrachloride + ethanol + smoking Dispositional effects: enhance uptake (eg. , ETOH + oral medications)

3. Potentiation: Toxicity of one chemical is increased in the presence of another, non-toxic chemical (0+4=10). egs. isopropanol + carbon tetrachloride croton oil + DMBA

4. Antagonism: Combined effect of chemicals is less than the sum of each chemical's effect alone. Chemicals can interfere with each other or one can interfere with the other (4+4=5; 4+ (-4)=0; 4+0=1). Functional produce opposite effects caffeine + alcohol

Chemical "inactivation" chemical reaction produces less toxic compound chelators (EDTA) antitoxins Dispositional alter disposition of compound (uptake, elimination, biotransformation) inhibit uptake (milk, activated carbon, oils) induction of enzyme systems Receptor "blockers" block or compete for receptors eg. , atropine blocks cholinergic receptor

Examples from terrestrial system There are basically two kinds of interactions between nutrients. SYNERGISM is a positive effect between nutrients and ANTAGONISM is a negative effect between nutrients. Two or more elements working together to create an overall improved physiological state in the plant is called physiological synergism while, excess of one nutrient reducing the uptake of another nutrient is called physiological antagonism.

These interactions depend on soil type, physical properties, p. H, ambient temperatures and proportion of participating nutrients. There is a highly controlled selectivity process involved in uptake of nutrients by plants and that is the reason why the plant does not contain the same ratio of nutrients inside the plant as found in the soil.

Synergism Many soil scientists, plant physiologists and plant biochemists have tried to clarify the much complicated relationships between nutrients. Some of these relationships are straight forward but, most are not. A few examples from agricultural laboratory research and field based experiments have shown us that an:

· Optimum supply of nitrogen ensures optimum uptake of potassium as well as phosphorus, magnesium, iron, manganese and zinc from the soils. · Optimal levels of copper and boron improve nitrogen uptake by plant. · Optimal levels of molybdenum improve utilization of nitrogen as well as increases uptake of phosphorus. · Optimal levels of calcium and zinc improve uptake of phosphorus and potassium. · Optimal levels of sulphur increases the uptake of manganese and zinc. · Optimal levels of manganese increases uptake of copper.

Antagonism · Excessive amounts of nitrogen reduce the uptake of phosphorus, potassium, iron and almost all secondary and micronutrients like calcium and magnesium iron, manganese, zinc and copper. · Excessive amounts of phosphorus reduces uptake of cationic micronutrients like iron, manganese, zinc and copper. · Excessive amounts of potassium reduce uptake of magnesium to a greater extent and calcium to a lesser extent.

· Excessive amounts of calcium reduces uptake of iron. · Excessive Iron reduces zinc uptake. · Excessive zinc reduces manganese uptake.

The examples above show that the interrelationships between nutrients in the plant system are quite complicated and interdependent. More research will need to be done on the molecular levels to elucidate the actual relationships if possible.

1. Toxic Unit Approach (Sprague, 1970). Additive Effect -- (x)TUA + (1 -x)TUB = 1 Synergistic Effect -- (x)TUA + (1 -x)TUB > 1 Antagonistic Effect -- (x)TUA + (1 -x)TUB < 1 2. Toxic Interaction Scale (S) (Marking and Dawson, 1975).

2. Toxic Interaction Scale (S) (Marking and Dawson, 1975). Toxic interaction scale is useful for binary mixtures of chemicals. The raw scale is non-linear, and calculated as: , where LC 50(a) and LC 50(b) are the LC 50 values for chemicals "a" and "b", respectively, LC 50(a|b) is the LC 50 value of chemical "a" in the presence of "b" and LC 50(b|a) is the LC 50 value of chemical "b" in the presence of "a". • Marking and Dawson modified "S" to conform to a linear scale, centered around zero: Indicative values of "S": S=1 additive S<1 synergistic S>1 antagonistic