I'm working on the following problem and would like some help. The current expert answer on here does not even match the problem:
Situation
Native Americans use forest plant species for food and ceremonial purposes. What is the risk to them if some areas of the US national forests and wildernesses where they collect these plants are sprayed with L7, a broadleaf and shrub herbicide?
Background
L7 is a systemic herbicide used to control deeply rooted herbaceous weeds and woody plants in rights-of-ways, forestry, rangelands, pastures, and small grains. L7 has been used for nearly 40 years. In forestry applications, as much as 1 lb active ingredient/acre of liquid is sprayed broadcast on foliage to open wildlife areas and rights-of-way. Only 1 treatment per year is allowed. Reentry into sprayed areas is allowed immediately after drying. Aerobic soil half-life is about 100 days.
Steps: Tier 1 Hazard and Dose-response Data
An acute oral LD50 evaluation was conducted in the rat. The LD50 was greater than 5000 mg/kg BW, so acute exposures are considered practically nontoxic. In a chronic toxicity feeding study conducted in the F344 rat, L7 was evaluated at 0, 20, 60 or 200 mg/kg BW/day for 2 years. The chronic toxicity LOEL was 60 mg/kg BW/day as evidenced by altered size and tinctorial properties of centrilobular hepatocytes and increased absolute and/or relative liver weights in both sexes. The Agency has classified L7 as Group E (evidence of non-carcinogenicity for humans). There is no evidence, based on the available data, to suggest that the chemical was associated with significant reproductive or developmental toxicity under the testing conditions.
A reference dose (RfD) for L7 was calculated to be 0.20 mg/kg BW/day based on a NOEL of 20 mg/kg BW/day from a two-year rat chronic feeding study. An uncertainty factor of 100 was used to account for the inter-species extrapolation and intra-species variability. The L7 chronic dietary exposure/risk estimates are extremely low. Because the dietary exposure/risk is so low, about 1/200th of the RfD, there are no concerns regarding chronic dietary exposure to L7.
Residue
Based on the application rate and the foliage type, the highly conservative estimated environmental residue is 135 mg/kg dry weight immediately after application.
Dietary Exposure
Consumption data on these forest plant species by Native Americans are lacking.
Risk Characterization Assumptions
รขยยข Max rate = 1 lb active ingredient/acre
รขยยข Body Weight = 70 kg (standard adult male weight used by US EPA)
รขยยข Chronic reference dose (RfD) = 0.2 mg/kg BW/d (this is the acceptable daily intake)
รขยยข Residue estimate = 135 mg/kg dry weight
รขยยข Adult enters the area immediately after spray dries
รขยยข Dietary Risk Quotient = Exposure รยท Toxic Endpoint, so for this example Dietary Risk = (Residue * Consumption Rate) รยท RfD
รขยยข Remember that a risk quotient (RQ) of 1 is where the exposure equals the toxic endpoint.
Questions
a. Given that specific consumption data are lacking for the treated plants, how would you estimate risk to Native Americans from consuming plants containing L7 residue?
b. The total vegetable consumption estimate per day in the US = 0.294 kg/70 kg adult (wet weight), or 0.06 kg/70 kg adult (dry weight). How can you use these numbers to help characterize the risk?
c. What refinements could be made to this dietary assessment?
d. What data elements are needed for higher-tiered aggregate assessments? Aggregate exposures include all possible routes and pathways of exposure to one chemical.
