Lifetime average daily exposure

Amortization of daily exposnre over the lifetime of an individual is another data analysis approach nsed by some jurisdictions. Although this value is not a true lifetime-average daily exposure estimate, and distorts the actual short-term exposure to higher values, the absence of a more accurate estimate has led the USA and Canada to use it by coupling with unit risk values for active ingredients considered as potential non-threshold carcinogens. 

Exposure Duration (weeks) Exposure Concentration Lifetime average daily exposure (pg/m ) Incidence of skin carcinomas... 

The ADD is the dose rate averaged over a pathway-specific period of exposure expressed as a daily dose on a per-unit-body-weight basis (US-EPA 1997). The ADD is used for exposure to chemicals with noncarcinogenic or nonchronic effects. Eor compounds with carcinogenic or chronic effects, the lifetime average daily dose (LADD) is used. The LADD is the dose rate averaged over a lifetime. The C refers to the concentration of the contaminant in inhaled air. The ED refers to the total time an individual is exposed to an air pollutant. 

The doses from exposure are characterized by distributions. For each possible dose level, these distributions quantify the probability that an individual in a specified population or subpopulation will receive that dose level as a result of exposure to atrazine and simazine through drinking water ingestion, dietary consumption, herbicide handling, or a combination of these potential exposure routes. For chronic toxic endpoints, the traditional (default) dose metric summarizing a lifetime of exposure is the lifetime average daily dose (LADD). Distributions of LADDs have been determined, and the corresponding distributions of the MOEs are presented herein. 

The potential for non-carcinogenic health effects associated with exposure of local residents to POPs in locally consumed food items and the ambient air was evaluated by calculating the relevant HQ for individual POPs. The HQ was defined as the ratio of the estimated lifetime average daily dose (LADD) of POPs from dietary (Table 7.6) and inhalation... 

The oral reference dose (Oral RfD) is an estimate of the daily exposure of a person to a contaminant that is likely to be without appreciable risk of a deleterious non-carcinogenic effect during a lifetime (USEPA http //www.epa.gov/iris/). Oral RfD values for POP concentrations in seafood types are presented in Table 16.5, together with the daily intake of POPs from seafood consumed in Singapore. Daily intakes of POPs from seafood are below the oral RfD. The cancer benchmark concentration (Dougherty et al., 2000) represents the exposure concentration at which a lifetime cancer risk equates to one excess cancer death in one million persons. This level is defined as the public health protective concentration in the Congressional House Report to the Food Quality Protection Act of 1996 in the USA. Cancer benchmark concentrations were exceeded for DDTs, heptachlor, and PCBs (See Table 16.5). The cancer hazard ratio is the ratio of the MDI for a specific contaminant relative to the cancer benchmark concentration. The cancer hazard ratio represents the extent to which average daily exposure exceeds the benchmark concentration. The cancer hazard ratio of seafood consumption... 

Figure 4 Relative contribution by exposure route to predicted dose Estimated population lifetime average daily dose of arsenic for children exposed to chromated copper arsenate (CCA)-treated wood playsets and decks in warm climate regions (from Zartarian et al., 2006).

In the Monte Carlo approach, there are no inherent limitations on the complexity of the exposure equation, the number of component variables, the probability distributions for the variable components, or the number of iterations. This freedom from limitations is especially useful in simulating the distributions of a lifetime average daily dose (LADD) for the different exposure scenarios considered herein. As its name suggests, a LADD is the average over all of the days in an individual s lifetime of the dose of a chemical (e.g. atrazine, simazine, or both) received by that individual in those days as a result of his or her exposure from one or more exposure pathways (e.g. water, diet and herbicide handling). Because the exposure equation can explicitly consider each day individually, the values of the equation s variable components can vary from day to day and have different distributions for different ages. The length of an individual s lifetime can also vary from individual to individual. 

Monte Carlo techniqnes allow the distributions of the LADDs for the combined exposure pathways for atrazine or simazine to be appropriately determined. It has been assumed herein that it is appropriate to add the absorbed doses from each route (ingestion, inhalation and dermal) and each pathway (drinking water, diet and herbicide handling) together. Thns, the LADD distribntion is the distribution among individuals of the lifetime average of the sum of the individual s daily doses from the different exposnre pathways and routes. The individual s lifetime average daily doses from the different pathways and rontes are summed, and then the distribution of these snms in a popnlation or snbpopnlation is determined. 

Lifetime average daily dose (LADD) Dose that is averaged over an individual s lifetime, taking into account the frequency, duration and intensity of exposure events. LADDs are usually expressed in units of mg/kg/d (USEPA,... 

In contrast to acute or short-term estimates of exposure, for purposes of chronic or long-term exposure and risk assessments, such as evaluation of potential lifetime excess cancer risk, regulatory agencies typically set the averaging time at that of an average lifetime (e.g., 70 or 75 years times 365 days year ) to obtain the lifetime average daily dose. 

To assess a carcinogen, doses are usually averaged over a lifetime and are presented as lifetime average daily doses (LADDs), even though exposure does not... 

Note The RSD is an estimate of tlie average daily dose of a carcinogen tliat corresponds to a specific excess cancer risk for a 70-yr lifetime exposure. 

Associated with daily time-weighted average arsenic exposure of >3.0 pg/m for 1 year Lifetime occupational exposure >54.6 pg As/m ... 

This no effect level is orders of magnitude higher than estimated human or environmental exposure. There are a number of recent estimates of the average daily lifetime exposure to DEHP which have been produced by a variety of authoritative bodies. These include ... 

A reasonable estimate of the average daily lifetime exposure to DEHP would therefore be 5 ng/kg body weight/day. 

For carcinogens, risks are estimated as the incremental probability of an indii idual developing ameer o er a lifetime as a result of exposure to the potential carcinogen. The slope factor (SF) converts estimated daily intakes averaged over a lifetime of exposure directly to incremental risk of an individual developing cancer. 

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