Avocado Girl

Refining measurements of pesticide residue

Sophie Harrington
Mar 30, 2016 · 5 min read

“The avocado girl.”

This is the first description I heard of Mona Hamdy, a new postdoc at CAIS’s Laboratory for Environmental Analysis. We take a quick drive to reach it, passing the architecturally impressive Whitehall Mansion on our way. When we enter the lab, LEA director and CAIS senior researcher Sayed Hassan greets us. Standing at one end of an aisle flanked by a swath of scientific instruments, he nods to a person hidden behind the clamor. A flash of pink bobs into view and out walks a bespectacled young woman whose deeply pink hijab contrasts nicely with her white lab coat. She smiles.

“Avocado girl” isn’t a comprehensive nickname. For one thing, “Avocado woman” would be more accurate, but perhaps less catchy. More importantly, Mona Hamdy came to CAIS from Egypt with a research proposal involving, but not restricted to, the fruit that’s taken America by storm. The avocado merely functions as an ideal variable for Mona’s central research question: which methods of extraction yield the best measurements of pesticide concentration?

In short, Mona takes avocados, spikes them with pesticides, and then runs various procedures to compare the quality of results from one method to the next. Why? Because once modes of pesticide extraction are refined, Mona can apply them to real world samples. Then she can confidently report whether or not their pesticide concentrations fall within the limits that The United States Environmental Protection Agency (EPA) sets on pesticide residue.

Mona Hamdy holding an avocado for future testing — Laboratory for Environmental Analysis

Pesticides’ bad wrap sprang out of Rachel Carson’s Silent Spring, published in 1962. The book, which provided evidence that the unchecked dispersion of DDT and other pesticides were hazardous to wildlife, catalyzed the modern environmental movement. The next few decades saw the establishment of the EPA, the U.S. ban on DDT for its carcinogenic properties, and the rise of a whole range of environmentally themed legislation and government organizations that continue today.

But agriculturalists have not abandoned pesticides. The world’s astoundingly rapid population growth demands that food production keep up, and it so happens that pesticides increase crop yield.

Yet these agricultural benefits clash with health detriments.

Just as chemotherapy attacks cancerous cells and healthy cells alike, pesticides attack the negative things, like crop-devouring insects, as well as non-target species, such as honey bees, butterflies, and us. Their brand of poison? Endocrine-disruptors that wreak havoc on the health of humans and wildlife by either blocking or over-stimulating hormone production. Hormones play significant roles in the body’s function, including the regulation of metabolism and nutrient supply; development and growth; and reproduction and sexual differentiation. So a substance that messes with hormone processes can have disastrous effects.

These health detriments weigh on Mona’s mind when she walks her market’s aisles. That’s what makes her research personal and pertinent.

Mona guides me over to an instrument the color of a Xerox. Known as GC-MS, it is the conjunction of a gas chromatograph and a mass spectrometer. This is how it works: Mona injects a solution containing her sample into the GC column. The sample vaporizes and a carrier gas pushes it through the column. During this process, the sample’s components separate based on volatility. Just like a football, a golf ball, and a bowling ball would roll down the same hill at different speeds due to their various shapes, sizes, and masses, so do these vaporized components move at different speeds as they are carried through the column.

Once completely separated, the components are transferred from the GC into the MS via another carrier gas, such as helium, nitrogen, or argon. The MS functions to identify target components via ionization — bombarding molecules with electrons to give them positive charges — and sorting them by mass via an electromagnetic field. Mona sets the range of mass she wants and the MS filters out the unwanted “noise,” sending the specified ions to a detector.

“The detector is like our eyes,” Mona said. It counts the ions and forwards the results to an accompanying computer in the form of a mass spectrum.

Mona must run samples through the GC-MS countless times, changing variables, comparing results to a standard, and tuning and retuning the instrument to ensure the most accurate analysis. Avocados are fat-rich, and that fat gets extracted with the pesticides, adding noise to the sample. Mona must test different adsorbents to eliminate as much fat as possible. The aim is to isolate pesticide components.

This is the point of transference from the Gas Chromatograph to the Mass Spectrometer. A non-reactive gas such as helium or argon carries the sample components from one machine to the next.

Trial after trial of handling and testing spiked avocado has turned Mona off from the food. There’s something repulsive about the mixture of pesticide stench with avocado smell. Soon, however, Mona will transition from just avocados to other fat-rich foods such as milk, fish, oils, olives, and nuts. She holds up a bag of some of the latter, explaining that these may be next in line. Mona expects to study the concentration of pesticides in addition to pharmaceuticals for her foreseeable future.

“I like the challenge,” she said. To make a trial, discover factors involved, refine the procedures, and to work toward a goal — it’s like a game with a central problem to be solved. “[You just need] to have the patience to reach what you want,” Mona said.

CAIS: Beyond the Lab

CAIS research helps us to fill in the gaps of human history, understand climate change, reveal misbranding of food products, and even trace the whens and wheres in crime investigations. Meet the people behind the science and learn more about how our research applies to you.

Sophie Harrington

Written by

A developing conservationist pursuing love and labor of land. Intentional rambler.

CAIS: Beyond the Lab

CAIS research helps us to fill in the gaps of human history, understand climate change, reveal misbranding of food products, and even trace the whens and wheres in crime investigations. Meet the people behind the science and learn more about how our research applies to you.

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