Biological Factors Affecting Toxicity

In plants, the most widely studied and probably the most important factor affecting their response to air pollutants is genetic variation. Plant response 

The sensitivity to 03 of two onion cultivars has been shown to be controlled by a single gene pair. Engle and Gableman (1966) showed that the resistant gene was dominant. They reported that after exposure to 03, the stomata of the resistant cultivar closed, with no appreciable injury, whereas the stomata of the sensitive cultivar remained open, with obvious injury. 

The sensitivity of plants is also affected by leaf maturity. Generally, young tissues are more sensitive to PAN and hydrogen sulfide, and maturing leaves are most sensitive to the other airborne pollutants. 

Genetic, developmental, health status, sex variation, and behavior are among the important factors affecting the response of animals and humans to pollutant toxicity (Hodgson 1980). 

---

Other factors affecting performance include the presence of toxic material, the redox potential, salinity of the groundwater, light intensity, hydraulic conductivity of the soil, and osmotic potential. The rate of biological treatment is higher for more permeable soils or aquifers. Bioremediation is not applicable to soils with very low permeability, because it would take a long time for the cleanup process unless many more wells were installed, thus raising the cost. 

These results have suggested that mineral dusts that are inert in a particulate form may have biological activity when they occur in a fibrous form. Factors affecting fiber toxicity include length, diameter, respirability resistance to chemical dissolution in biological fluids, and durability. "... 

The factors affecting the disposition and toxicity of a foreign compound may be divided into chemical and biological factors. 

There are many factors, both chemical and biological, which affect the disposition of xenobiotics. Chemical factors include size and structure, pKa, chirality, and lipophilicity. Biological factors include species, sex and strain, genetic factors, hormonal influences, disease and pathological conditions, age, stress, diet, dose, enzyme induction and inhibition, and tissue and organ specificity. All of these factors can affect the toxicity of a chemical by changing its disposition, especially its metabolism. 

Several factors affect the selection of the buffer solution, such as the optimum pH the buffer anionic or cationic species (which can interfere in the subsequent purification steps) the pH variation with ionic strength or temperature the buffer reactivity with the proteins in solution the biological activity (e.g. phosphates can inhibit or activate a protein in biological reactions) the interaction of the buffer with other components the buffer permeation in biological membranes the toxicity the light absorption at 280 nm the cost (especially if used in large-scale processes) and the protein solubility. 

While chemical composition is important in determining the toxicity of particles and fibers, it is equally or more important to determine where a particle or fiber will deposit in the respiratory tract and how long it will stay there. The quantity and location of particle deposition in the respiratory tract depends on factors related to both the exposed individual and the inhaled particles. The mechanism of deposition is determined by the physical (size, shape, and density) and chemical (hygroscopicity and charge) characteristics of the inhaled particles. Particle deposition is also affected by biological factors inherent to the exposed individual such as breathing pattern (volume and rate), route of breathing (mouth versus nose), and the anatomy of the airways. 

Although variability is inherent in all environmental measurements, a variety of physical, chemical, and biological factors should be noted in compliance biomonitoring to enhance the consistency and de-fensibility of toxicity test results. These various parameters may affect the effluent toxicity to aquatic biota, and it is important that the investigator take them into account. Test conditions should mimic receiving water conditions, whenever feasible, to allow accurate assessment of the in-stream effect of an effluent. However, the use of upstream water for dilution should be avoided due to the potential variability in quality, or toxicity, over the testing period. 

Just as there are a large number of pollutants in our environment, so there are many factors that affect the toxicity of these pollutants. The major factors affecting pollutant toxicity include physicochemical properties of pollutants, mode of exposure, time, environmental factors, interaction, biological factors, and nutritional factors. These parameters that modify the toxic action of a toxicant are examined in this chapter. 

Biological methods measuring toxicity or bioaccumulation are currently used widely to indicate bioavailability, yet interpretation of the results can be confounded by factors unrelated to bioavailability. For example, estimates of toxicity can be modified by the organism s general health, acclimation or adaptation. Bioaccumulation as a measure of bioavailability is confounded by behavior-affected exposure (such as feeding and respiration rates) as well as by metabolism of the contaminant of interest (USEPA, 1998). 

It is likely, in the case of Echo Lake, that the loss of certain fish populations were acid-induced however, the apparent atmospheric washout and the intermittent Presence of residual oxidants in this natural water body raise new questions on the potential impact of synergistic effects of microcontaminants on biological organisms at depressed pH s. Experimental evidence has shown that oxidant residuals are toxic to freshwater organisms (Brungs, 1973). Further research is needed to determine the exact nature of these microcontaminants and examine the significance of these residual contaminants as an additional factor affecting food web yield and population structure. 

---