A survey was made to determine the levels of insect damage and rodent excreta pellets in wheat. The analytical data obtained represented the various grade designations of wheat normally encountered during wheat grade certification in the 34 Agricultural Marketing Service, Grain Division, field offices. The mean and range of weights of insect-damaged kernels per 100 g and rodent excreta pellets and pellet fragments per kilogram were 71.5 mg (0–3809 mg) and 0.9 mg (0–100 mg), respectively. The mean and range of numbers of insect-damaged kernels and rodent excreta pellets were 3.3 (0–169) and 0.1 (0–11), respectively. The percentages of samples containing insect-damaged kernels and rodent excreta were approximately 35 and 7%, respectively.

A collaborative study has been completed on an improved method for the detection and confirmation of uric acid from bird and insect excreta. The proposed method involves the lithium carbonate solubilization of the suspect excreta material, followed by butanol-methanol-water-acetic acid thin layer chromatography, and trisodium phosphate-phosphotungstic acid color development. The collaborative tests resulted in 100% detection of uric acid standard at the 50 ng level and 75% detection at the 20–25 ng level. No false positives were reported during tests of compounds similar to uric acid. The proposed method has been adopted official first action; the present official final action method, 44.161, will be retained for screening purposes.

The official method for urine-contaminated grains, 36.109, has an inherent weakness because of the lack of total contact between the test object and the test paper. The modified method virtually eliminates this weakness by embedding the grain in a soft agar containing urease and bro mo thymol blue; the sensitivity is about 2.5 μg urea distributed over a grain of wheat. This is comparable or slightly better than that for 36.109; however, the chances of detection of random spots is better than the AOAC method because of the total contact of the test object with the test medium.

Follow-up experimental work of the 1971 preliminary method study revealed the need for a change in sample size, an improved extract cleanup technique, and the identification of a urine-specific metabolite. A modified method collaboratively tested in 1972 is capable of handling a larger sample in the Soxhlet extractor. The extract is cleaned of interfering substances by chromatography with an appropriate solvent prior to 2-dimensional TLC. The indicator metabolites, urea, allantoin, and indican, are detected by sequential sprays. The collaborative study resulted in 90% correct positive determinations with no false positives. The minimum detection level is approximately 2 μl urine/9 g wheat. The method has been adopted as official first action.

Recommendations are made to delete sections 40.131–40.132, the urease-bromothymol blue paper test, and t o revise method 40.A09–40.A10 to reflect improvements in manipulations and reagent stability. The warm 1% agar is replaced by a 0.25% agar with a mold inhibitor and is useful up to 4 months.