Evaluating Concentrations of Pesticides and Heavy Metals in the U.S. Peanut Crop in the Presence of Detection Limits

Overview

Blair and Lamb analyzed mercury, cadmium, lead, and arsenic in U.S. peanut crop samples collected at farmer-stock buying points during the 2013-2015 crop years. The sampling design covered three major U.S. growing regions and used censored-data methods for analytes with results below detection limits. The arsenic testing did not differentiate organic from inorganic forms, so arsenic is treated here as total/unspecified arsenic.

Key numbers

Table 1 reports 290 heavy-metal samples across 16 buying points: Southeast runner peanuts from 10 buying points (71 samples in each of 2013, 2014, and 2015), Southwest runner/Virginia/Spanish peanuts from 3 buying points (15, 12, and 16 samples by year), and Virginia-Carolina runner/Virginia peanuts from 3 buying points (12, 12, and 10 samples by year).

Table 8 summarizes population mean estimates and 95% upper confidence limits in ppm:

Cadmium had no censored observations. Table 2 reports the all-year/all-region cadmium (Cd) minimum 0.020 ppm, maximum 0.328 ppm, mean 0.0768 ppm, 95% confidence interval ( 0.0714, 0.0821 ), and UCL95 0.0814.

Arsenic was censored below 0.02 ppm. Table 3 reports all-year/all-region arsenic with 109 censored observations out of 290, maximum 0.41 ppm, ROS mean 0.0282 ppm, 95% confidence interval ( 0.0258, 0.0312 ), and UCL95 0.0308. The article states that the 0.41 ppm sample in 2015 was a Southwest-region outlier.

Lead was censored below 0.02 ppm. Table 5 reports all-year/all-region lead with 94 censored observations out of 290, maximum 0.64 ppm, ROS mean 0.0322 ppm, 95% confidence interval ( 0.0282, 0.0377 ), and UCL95 0.0367. The 0.64 ppm value was a 2013 Virginia-Carolina outlier.

Mercury was too heavily censored for a mean estimate. Table 7 reports probability intervals for testing below the 0.01 ppm detection limit: 2013 all-region samples had 98 censored results out of 98, with interval ( 0.970, 1.00 ); 2014 had 88 out of 95, with interval ( 0.854, 0.970 ); 2015 had 95 out of 97, with interval ( 0.927, 0.997 ).

Methods (brief)

Samples were collected during farmer-stock grading at 16 buying points across three crop years. Each 2 kg sample was composited and homogenized by Eurofins. Heavy metals were measured by ICP-MS on a Perkin Elmer NexION 300D after microwave-assisted acid digestion with nitric acid and hydrogen peroxide. NIST SRM 1568B and 1515 were analyzed as laboratory control samples, and recoveries for analytes of interest were within 10% of 100. For arsenic, the testing did not differentiate between organic and inorganic forms. The analysis used Kaplan-Meier, regression on order statistics (ROS), and maximum likelihood estimation for censored observations, with discussion focused on ROS results.

Implications

This source provides U.S.-market peanut occurrence evidence for Cd, total/unspecified arsenic (As), lead (Pb), and heavily censored total/unspecified mercury (Hg). The routeable peanut values are national crop-level mean estimates and UCL95 summaries, not single-state or product-brand measurements. Mercury should remain as censored total-Hg context because the source does not provide a concentration distribution suitable for mean estimation and does not measure methylmercury.

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