Dermal response curves

Table I was constructed according to the procedure of Knaak et al. (3) using the dermal dose-ChE response curves in Figures 4 and 5. Paraoxon was used as the pesticide standard for methidathion and chlorthiophos, while azinphosmethyl oxon was used as a standard for chlorthiophos oxon sulfoxide and methidathion oxon. The groupings are based upon similar slope values for the dose-response curves. Parathion and azinphosmethyl acted as their own standard. A standard is a pesticide for which safety information is available. In this Table, safe levels are given for the thions and their respective oxons. The safe level for total residues (thion + oxon) lies between the safe levels for the thion and its oxon if the oxon level is at or below its safe level.

Table I. Establishment of Safe Levels on Tree Foliage (in ug/cm ) Using the Results of Dermal Dose-ChE Response Curves and Field Reentry Studies according to Knaak et al. (3)...

Figure 4. Dermal dose-ChE response curves according to Knaak et al. (3, 9). Male Sprague-Dawley rats weighing 220-240 g were used. A 25-cm2 area of skin was treated. Red blood cell ChE was determined 72 h after the application of the OP...

Dermal Dose-Response Studies. The dermal dose red cell ChE-response curves for parathion and thiodicarb are given in Figure 2. Para-thion, the most toxic pesticide used, inhibited 50Z of the red cell ChE activity at a dose level ot 31 t%/cm (3.2 mg/kg) of treated skin in 72 hr, tdiile 322 ug/cm of thiodicarb (33.3 mg/kg) gave 50 ChE inhibition in 24 hr. Carbaryl at dose levels up to 4,000 ng/cn of treated skin (417 sig/kg) did not produce detectable ChE inhibition 24 hr after application of the dose. Thiodicarb was dermally more toxic than carbaryl, but substantially less toxic (1/10) than parathion. 2... 

Determining anticipated route and magnitude of exposure is an important component in the overall assessment of safety and must be done on a nanomaterial-by-nanomaterial basis, with secondary exposures taken into consideration when necessary. The estimated exposure levels for a nanomaterial may then be compared with the calculated safe dose derived from the hazard identification evaluation. The procedures and factors considered in the exposure assessment process are not expected to be any different for nanomaterials than for larger particles or chemicals. The degree of hazard associated with exposure to any chemical or substance, regardless of its physicochemical characteristics, depends on several factors, including its toxicity, dose-response curve, concentration, route of exposure, duration and/or frequency of exposure. However, depending on the route of anticipated exposure (dermal, inhalation, oral) and types of associated toxicities (local or systemic), a chemical may not pose any risk of adverse effects if there is no... 

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