Simazine drinking water ingestion

Even when an individual s atrazine and simazine intakes from drinking water ingestion (water) and food consumption (diet) were combined, 95% of the MOEs exceeded 30000. The minimum acceptable MOE for human environmental exposure is usually in the range between 10 and 1000 so the atrazine and simazine MOEs provide an ample safety margin. For atrazine and simazine combined, 95% of the MOEs are in excess of 38000 for water alone and in excess of 280000 for diet alone. 

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. 

Figure 31.1 The distribution of the MOEs associated with atrazine and simazine from drinking water ingestion in the 18 major atrazine-use states combined. Based on drinking water data prior to June 1, 1994.

Figure 31.12 Distributions of the MOEs for simazine from drinking water ingestion, dietary consumption, and both exposure pathways combined.

Figure 31.14 Distributions of the MOEs for simazine herbicide handlers involved in com production from their use of flowable formulation or WDGs and from their herbicide handling combined with both drinking water ingestion and dietary exposure.

Distributions of the MOE have been presented for individual exposure pathways (drinking water ingestion, dietary consumption, and herbicide handling), for the combined exposure pathways, and for atrazine and simazine both separately and combined. The MOEs have been calculated using a lower bound on the ED10 for the most sensitive effect in the most sensitive sex, strain, and species studied in chronic animal bioassays (i.e., mammary tumors in female SD rats). This mammary tumor response in the SD rat is not relevant to humans (IARC, 1999 United Kingdom, 2000 USEPA, 2003 Australia, 2004). 

The exposure from each of the routes of exposure (drinking water ingestion, dietary consumption and herbicide handling by workers) is described by an equation in the atrazine and simazine assessment. Some of the components of these equations have values that are variable (e.g. from individual to individual, from one year to the next, from one serving of a specific food to another serving, and from one handling of a herbicide to another handling). These variable components of the exposure equations are described by probability distributions that reflect the relative frequency of the different values for the variable. 

Figure 8.1 The distributions of the margins of exposure associated with (a) atrazine and (b) simazine and drinking water ingestion in the 18 major major-use states combined...

Figure 8.15 Distributions of the margins of exposure in the USA for atrazine and simazine combined from drinking water ingestion (W), dietary consumption (D) and both exposure pathways combined (W - - D)...

Figure 8.16 Distributions of the margins of exposure for US herbicide handlers who apply either atrazine or simazine and who are also possibly exposed to both atrazine and simazine via the water and dietary pathways FFs, flowable formulations WDGs, water-dispersible granules W, drinking water ingestion D, dietary consumption HH, herbicide handler...

Distributions of the MOEs have been presented for individual exposure pathways (drinking water ingestion, dietary consumption and herbicide handling), for the combined exposure pathways, and for atrazine and simazine, both separately and combined. 

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. 

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