Dietary risk assessment

Risk assessments are routinely performed to assess the safety implications for the intentional or unintentional presence of low-molecular-weight chemicals in food and feed. The procedures and mathematical models used to predict risk have evolved over the years and have been extensively reviewed.97-99 The dietary assessment includes both acute and chronic exposure assessments. Acute exposure assessments address short-term exposures using approximately 95th- or 97.5th-percentile food consumption data (where available) and acute toxicity data generated with the low-molecular-weight chemical. Some, however, may question the use of acute dietary risk assessments for proteins when there is no evidence that they are acutely toxic. Chronic exposure assessments use mean (50th-percentile) food consumption data and use the lowest no-effect level from the battery of toxicology studies to establish an acceptable daily intake (ADI) for the low-molecular-weight chemical added to food. Calculation of an ADI has not been considered necessary for certain proteins such as the Cry insecticidal proteins. Cry proteins, whether introduced into biotech food crops, or sprayed on food crops as components of commercial microbial pesticide formulations, have generally been exempted from the requirement of a tolerance.

The same procedures have been used for preparing dietary risk assessments for proteins introduced into biotechnology-derived food and feed crops. The dietary intake of the introduced protein can then be estimated by multiplying the intake estimates by the concentration of the introduced protein in the food. Chapter 9 provides lists of food consumption databases that are available for various countries. Some food consumption data is based on the annual disappearance of food within the borders of the country, which is divided by the overall population to estimate daily intake of the food commodity. These databases overestimate daily intake of the food by adults. The more accurate consumption databases are based on survey information of individuals over 24 to 48 hours. This information can be collected for both adults and children. There is a need for countries to develop more comprehensive food survey data on their respective populations so that dietary risk assessments can be more accurately performed. At present, 95th- or 97.5th-percentile food consumption data are only available for certain countries such as the United States, the UK, and Australia. However, as shown in Chapter 9, a number of countries have been carrying out food consumption surveys and it is hoped that this will be more publicly available for those that have a need for this information to carry out dietary risk assessments. An example for a dietary risk assessment for YieldGard® Cornborer (Monsanto Technology, LLC.), an insect-protected, biotechnology-derived crop is provided below.

CrylAb protein derived from Bacillus thuringiensis (Bt) was introduced into corn plants to provide protection against corn borer pests that damage both the stalk and ears. The levels of Cry1Ab protein in leaf and stalks is around 12 ppm, and in grain, 0.3 ppm.100 As shown in Table 11.1, mice were dosed up to 4000 mg/kg with Cry1Ab protein and experienced no adverse effects.

1. Acute Dietary Exposure Assessment

• The 97.5th-percentile corn endosperm* fraction consumption in the UK for adults is 113 g/person/day ■ 70 kg body wt/person = 1.6 g/kg.

• The 97.5th-percentile adult dietary intake of Cry1Ab protein would be: 1.6 g/kg/

day x 0.3 mg/g corn = 0.48 mg/kg for an adult (0.00048 mg/kg).

• The margin of safety for acute exposure to Cry1Ab protein is 4000 mg/kg ■ 0.00048 mg/kg = 8,333,333 X.

Put another way, a 70-kg-body weight human adult would need to consume > 900,000 kg (900 metric tonnes) of grain in one day to attain the same acute dosage (4000 mg/kg) of Cry1Ab protein given to mice which produced no adverse effects.

2. Chronic Dietary Exposure Assessment

• The average (50th-percentile) corn consumption in the UK for adults is ~16 g corn/ person/day ■ 70 kg body wt/person = 0.23 g/kg.

• The average adult dietary intake of Cry1Ab protein would be: 0.23 g/kg/day x 0.3 mg/g corn = 0.07 mg/kg for an adult (0.00007 mg/kg).

• The average rat dietary intake of Cry1Ab protein in a 90-day feeding study is 25 g corn/kg BW x 0.3 mg/g corn = 7.5 mg/kg

• The margin of safety for chronic dietary exposure to Cry1Ab protein is 7.5 mg/kg divided by 0.07 mg/kg = 107 X

This dietary exposure assessment makes some very conservative assumptions. It assumes that 100% of the corn consumed in the diet is YieldGard® Cornborer that contains the Cry1Ab protein. In reality, many varieties of corn are sold commercially, so that YieldGard® Cornborer represents only a fraction (~20%) of the total corn varieties consumed in the diet (as of 2002).101 It also assumes that the Cry1Ab protein is not denatured by thermal processing of corn grain into food products. Soybeans are both heat-processed to inactivate trypsin inhibitors and solvent-extracted to remove oil. Processing denatures proteins like CP4 EPSPS, which have been introduced into soybeans to impart tolerance to glyphosate herbicide.

The dietary risk assessment shown above uses corn consumption data for adults in the UK. If a dietary risk assessment was prepared for Central America, the safety margin would be somewhat lower, as corn consumption is hundreds of grams per person per day.102 However, the safety margin would still be very large since the level of Cry1Ab in corn grain is very low. Thus, risk assessments can be tailored for individual countries when there are accurate food consumption data available.

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