the market as sophisticated copies, with high-quality branding and packaging that can pass for the legitimate product. Application of adulterated or counterfeited pesticides can adversely affect crop growth. Pesticides are sold according to a labeled concentration of the active ingredient.

An issue raised by Haggblade et al. (2018) in their work on pesticides in Mali is the widespread presence of unregistered pesticides in markets, including pesticides that are registered in other neighboring countries but not in Mali and pesticides with no registration in the region. Haggblade et al. also document the presence of pesticides with banned ingredients in Mali including pesticides containing atrazine and paraquat. Murphy et al. (2012) evaluate the contents of 128 samples of pesticides purchased in The Gambia and find most products are unlabeled, sold in plastic bags or unlabeled plastic containers; they find a wide range of pesticides for sale, nearly half of which contained components that are banned by the World Health Organization or in the United States.

# **IV. Fertilizer Quality Measurement and Evidence**

# **Measuring Agronomic Quality**

Lab-based measures are required for accurate assessment of fertilizer nutrient content. Nitrogen has measurement requirements that are distinct from other nutrients. The International Fertilizer Development Center (IFDC) uses Inductively Coupled Plasma-Optical Emission Spectrometry (ICPOES) to measure potassium (K2O), Calcium (Ca), Magnesium (Mg), Zinc (Zn), Boron (B), and Cd (Cadmium) in fertilizer samples and has used both the Kjeldahl method and combustion analysis to measure nitrogen (N) and sulfur (S) (Sanabira 2013; Sanabria 2019a; Sanabria 2019b). Note that determining adulteration once the nutrient content is found to be out of compliance requires a further analysis step to identify and document the presence of non-fertilizer material fillers; this step is essential in order to distinguish adulteration from errors in manufacturing. In addition, best practices for fertilizer testing include calculation and reporting of the analytical error, which is the error from the chemical analysis itself. Analytical error can be due to instrument malfunction (due to miscalibration for example) or analyst error and is calculated by double-testing samples and comparing the results. Several recent research studies have used two separate labs to test the same samples to assess differences in the analytical error across labs. Ashour et al. (2019a) for example sent 115 samples of urea fertilizer and 72 samples of NPK to both a Ugandan lab – which used the Kjeldahl method - and to a lab based in the United States – which used combustion (also known as the Dumas method) – and the results were substantially different.<sup>13</sup> Michelson et al. (2021) shipped samples from Tanzania, where facilities for measurement of nitrogen content were limited, to both Kenya and to the United States for testing. Ten percent of the samples were tested in both labs. Initial results from the Kenyan lab suggested significant and widespread nutrient problems in the samples but these results were not consistent with the lab results for the same samples from the United States. All samples were subsequently reanalyzed in the Kenyan lab with re-calibration based on results from the US labs. This

> 13 While the Ugandan lab found wide variation in the nitrogen content of both the urea and NPK samples; between 20% and 70% nitrogen in the urea and between 5% and 30% for the NPK, the US-base lab found that nearly all urea samples contained 46% nitrogen and that nearly all NPK contained 17% nitrogen.

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