Contamination of Pesticide residues and Human Health Risk Assessment of the Selected Agricultural Soils in Oyo State, Nigeria

The Invisible Garden Party

Imagine your backyard soil as a giant, busy dance floor. For decades, farmers have invited special guests to this party: pesticides. These are chemical bodyguards designed to stop bugs from eating crops, but like rowdy partygoers who refuse to leave, some of these chemicals get stuck in the dirt long after the party is over. In the world of science, this is called "contamination," and the specific guests we are worried about are "pesticide residues." Some of these guests are old, stubborn, and banned from the party (like organochlorines), while others are newer, faster, and still being invited (like pyrethroids). The big question scientists ask is: "How much of this chemical mess is actually on the dance floor, and is it dangerous for the people living next door?" This isn't just about dirty dirt; it's about whether the food grown in that dirt, or the dust kicked up from it, could make people sick.

The Chemical Detective Story in Oyo State

In this study, a team of scientists from Lagos State University of Science and Technology acted as chemical detectives in Oyo State, Nigeria. They traveled to two farming regions, Ibarapa and Oke-Ogun, to investigate the soil in four specific towns: Araromi, Jakode, Itasa, and Oke-Ola. They wanted to know if the soil was hosting a secret, toxic party. To do this, they didn't just look at the dirt; they took samples from the top 20 centimeters (about 8 inches) of the ground—the "root zone" where plants drink and where chemicals hang out. They collected ten tiny bits of soil from each spot, mixed them into one big "composite" sample, and sent them to a high-tech lab.

Using a super-sensitive machine called Gas Chromatography–Mass Spectrometry (GC–MS), which acts like a microscopic fingerprint scanner, the team searched for two main groups of chemical guests: Organochlorines (the old, banned, stubborn ones) and Pyrethroids (the newer, currently used ones).

What They Found: A Mixed Crowd of Unwanted Guests

The results were a bit like walking into a room where the old, banned guests never left, and the new guests just arrived. The scientists found that multiple residues were detected in all sites, though not every single chemical was present in every single spot. It wasn't just one or two chemicals; it was a whole mix.

• The Old Guard (Legacy Contamination): They found high levels of "organochlorines" like heptachlor, aldrin, dieldrin, and endosulfan. These are chemicals that were banned a long time ago because they are dangerous and don't break down easily. The fact that they are still there, sometimes at levels as high as 1.33 ppm (parts per million) for heptachlor epoxide, proves that these chemicals are like ghosts that refuse to fade away.
• The New Guard (Current Inputs): They also found "pyrethroids" like lambda-cyhalothrin and cypermethrin. These are chemicals farmers are likely still using today. The highest levels of these were found in Jakode and Araromi.

The scientists used a special kind of math (called Principal Component Analysis and Cluster Analysis) to sort these chemicals. They discovered that the chemicals weren't just randomly scattered. Instead, they formed tight-knit groups: the old, stubborn chemicals stuck together, and the new, active chemicals stuck together. This confirmed that the soil is dealing with a "double dose" of pollution: the leftovers from the past and the fresh applications from the present.

The Danger Zone: Is It Safe?

The most critical part of the study was asking, "Is this safe for humans?" The scientists compared the amount of poison they found in the soil against the safety limits set by the World Health Organization (WHO) and the Food and Agriculture Organization (FAO).

The news was not good.

• The Limits Were Broken: Several analytes exceeded the safe limits in all locations. For example, the safe limit for heptachlor is 0.01 ppm, but they found up to 1.10 ppm. That is over 100 times the safe limit!
• The Risk Score: They calculated a "Risk Quotient" (RQ) to see how dangerous the exposure is.
  • Heptachlor epoxide and dieldrin had "Critical" risk levels, with scores ranging from 3,400 to 13,300.
  • Aldrin and Endosulfan had "Very High" risk levels, with scores between 820 and 1,550.
  • Even the newer chemicals like Lambda-Cyhalothrin had "High" risk scores.

To get a clearer picture of the danger, the team ran a computer simulation called a Monte Carlo simulation. Imagine rolling dice 10,000 times to see how likely a disaster is. In this case, the simulation showed that there is a greater than 90% probability that the risk to human health exceeds safe levels under realistic exposure assumptions. In other words, it is highly likely that people in these areas are being exposed to dangerous levels of these chemicals.

The Hotspot and the Conclusion

The study also mapped out where the trouble was worst. They found that Jakode was a "hotspot," meaning it had the highest concentration of these toxic chemicals compared to the other towns.

The researchers concluded that the soil in these farming areas is not just dirty; it is a long-term storage tank for dangerous chemicals. The problem isn't just one bad apple; it's a whole basket of them. The soil holds onto the old, banned chemicals while simultaneously soaking up new ones. Because these chemicals can move from the soil into the food we eat or the air we breathe, the study suggests that the current way of farming and managing these chemicals is putting human health at serious risk. The scientists recommend that authorities stop treating these chemicals as separate issues and instead focus on the "mixture" of toxins, especially in hotspots like Jakode, to protect the people living there.