1. The genetically engineered foods and drugs first go through animal testing; this will tell us about any biological effects of the product, that it may have. Then they have to go through human testing (once it is clear that it is a safe food or drug for an animal). The FDA clearance is not required for the food supplements like the vitamins becaus ethey are made up of natural ingredients and they will not have any adverse side effects. Yes, again the additional rules for geneticall engineered foods and drugs produced by genetically enginerreed organisms include animal testing prior to humnan testing. These rules do offer sfatey of humans using genetically enginereed products.

2. yes, the concepts of NOAEL and LOAEL are compatible with the threshold level or a no threshold level conception of dose responses. The threshold point on the dose-response curve represents a dose point below which there is no reponse is seen. The NOAEL is the higest non-statistically significant dose tested point and LOAEL is the point at which yhe lowest dose is tested with observable effects. This curve differs from the zero response curve in that the intial dose is greater than zero.

3. Thyroid gland, which produce the thyroid hormones are a apossible target for PCB (polychlorinated biphenyls) toxic effect. These hormones have effect on cardiovascular system. Hypothyroid is associated with the decreased heart rate, contractility and hyperthyroid is associated with the increased heart rate. The PCB can act during development to lower the thyroid hormone and cause metabolic defects. The PCB can also target the nervous system (neurobehaviral) by affecting the spatila leraning ability (C &D, 369). The immune system can also be a target for PCB. Severe atropphy of primary and secondary lymphoid organs, immunosuppression and tumor promotion are only few examples of effects that can be cause by PCB on immune system. Yes, there will be other targets if we include the molecular clearance pathway for PCB. This pathway might act as a cascade where certain genes might be turned on and others might be turned off due to this pathway. The amine derivative of PCB like nitro amines (N-nitrodimethyl amine (DMN)) can have effects on immune system too. Most of the derivatives of the PCB have similar effects (not identical).

4. Acute exposure refers to a single exposure administrtaion of a toxin. Repair functions interfere wit hthe analysis of toxicity in acute exposure because if any toxicity result from a single exposure, it will be repaired quickly byu a repiar function and it will be hard to detect any adverse effects of the drug being administarted. Chronic exposure on the other hand, refers to exposure of a drug for more than 3 months (C &D, 14). Well, in this case the adverse effects of the toxin or a drug may be a lot and the repair function might not be able to fix it all. The toxic effects of the drug might be known, atleast to some extent. Therefor, the acute exposure damage might be repaired and therefore the toxic effects of the toxin could not be analyzed.