Improving Risk Assessment and Regulation of Food Contaminants Using Novel Methods to Estimate Cumulative Dietary Exposure and Establish Safety Levels

Abstract

The presence of chemical contaminants in food has received considerable media attention due to consumers’ increasing demands for safe, nutritious and high quality food. The issue is controversial and complicated, and scientific findings regarding chemical contaminants in foods are often misinterpreted, presenting challenges for consumers, legislators, scientists, the food industry and government agencies. This dissertation explores new methodologies to improve risk assessment and regulations for food contaminants based on scientifically rigorous methodology to estimate dietary exposure and establish safety levels for contaminants and pesticide residues in food.

The first and second chapters of this dissertation provide an assessment of the US dietary exposure to total and inorganic arsenic and a review of arsenic exposure identifying the main sources of arsenic in food, the health effects associated with dietary arsenic exposure, the implications of arsenic for the food industry, and challenges that must be addressed. Toxicologically, arsenic health effects are principally attributed to the inorganic forms of arsenic, but most analytical methods provide results for total arsenic (organic and inorganic) and can lead to overestimations of actual dietary risk to arsenic.

Nine scenarios were designed to estimate levels of inorganic arsenic found in food samples collected from the US Food and Drug Administration’s Total Diet Study and analyzed for total arsenic. The different scenarios made different assumptions regarding the percentage of total arsenic that was present as inorganic arsenic in terrestrial and marine food forms. Children represented the population subgroup that received the greatest inorganic arsenic exposure and the primary food groups responsible for their exposures were grains, legumes, seeds, and beverages. All the exposures estimated obtained for the population subgroups studied were below the U.S. Environmental Protection Agency established reference dose of 0.3 ug/kg/day for inorganic arsenic.

The third chapter explores the relationship between pesticides tolerances/MRLs and safety. Tolerances and MRLs are perceived erroneously as parameters of safety and a novel approach to evaluate pesticide residues in term of health significance is proposed. A simple example based on one pesticide (captan) on one commodity (strawberries) was developed to present the proof of concept for Pesticide Food Safety Standards. This parameter better explains the health significance, if any, based on the level of pesticide residues in food and demonstrates that violative pesticides residues above the tolerance or the presence of pesticide detected on a food for which no tolerance or MRL is established are rarely of health significance.

The fourth chapter of this dissertation presents a cumulative dietary exposure for organophosphate pesticides from fruits and vegetables in the United Sates. Organophosphate pesticides share a common mechanism of toxicity and many different members of this family of pesticides are frequently used in agriculture. They can be characterized as having a relatively high acute toxicity and are considered to represent a group of pesticides most likely to be associated with posing dietary risks to consumers if they are not used properly. Cumulative exposure estimates for organophosphate pesticides were performed that considered all members of the family rather than exposure assessments focused on individual organophosphates. Exposure estimates used traditional methods of cumulative exposure analysis by considering relative potencies of organophosphates based on benchmark doses and No Observed Adverse Effects levels, and a novel approach used to determine relative potencies based on the Lethal Dose 50 (LD50) of the pesticides involved was developed. Studies also investigated the influence of the choice of the index chemical used to determine relative potencies among the pesticides studied. The novel LD50 approach presented some advantages compared with the other approaches, particularly with respect to the availability and accuracy of toxicological data. All the exposures estimated at the 99.9th percentile represented an insignificant risk for the US population including children. These findings suggested that the presence of high levels of pesticide residues in specific food items are more likely due to a misuse of the pesticide and the additional exposure from other residues present in others food items do not significantly impact the exposure assessment.

In the fifth chapter, a novel approach used to calculate “Pesticide Safety Levels” for organophosphate pesticides in foods is presented. Pesticide Safety Levels, representing levels of individual organophosphates on individual commodities that could trigger safety concerns, were calculated for 54 organophosphates on 80 fruit, vegetable, and nut commodities. Comparisons of Pesticide Safety Levels with tolerances and MRLs indicated that Pesticide Safety Levels were more than 100 times higher than tolerances/MRLs in the majority of cases where comparisons could be made, while a small number of Pesticide Safety Levels were equal to or slightly lower than tolerances/MRLs. Pesticide Safety Levels are important as they provide information regarding the differences between tolerances/MRLs and safety, because they can help determine the health significance, if any, for organophosphate residues that exceed tolerances/MRLs or are detected on commodities for which tolerances/MRLs have not been established, and because they can help guide residue monitoring programs to focus more upon safety than upon tolerance/MRL enforcement. They can also be modified for different regions of the world based upon different food consumption patterns.