What is the Impact of Herbicide Overuse? - Chromatography Investigates

A recent report in the Port Harcourt Medical Journal - The effect of the application of different rates of herbicides on the residual level of the herbicides and their metabolites in harvested maize cobs – has looked at the residual levels of herbicides in maize crops to see if excess herbicide use could leave high levels of herbicides in the crops affecting human health, crop yield and the environment.

Weeds of choice

With an ever-growing population that needs feeding, it is important that farmers can achieve the maximal crop yield per hectare for all crops. One factor that affects the crop yield is when weeds grow amongst the crop. Weeds affect crop growth through competition for resources – nutrients, water, space and sunlight. Weeds grow where the conditions and environment suit them – sometimes the environmental conditions might suit the weeds more than the crop of choice.

In Nigeria, the traditional method of controlling weeds was carried out by using mechanical methods using hoes or pulling weeds up. But the method is time consuming and labour is expensive, especially during the peak growing season. So, growers started using chemical methods of weed control, namely herbicides which are quicker, less expensive and easy to apply.

Growth in herbicide use

Reports show an increased use in herbicides in Nigeria in the last ten years – ad this has shown some increases in crop yields. But many workers are unskilled in the use of herbicides, with many farm workers illiterate and so there is little knowledge regarding the actual use of herbicides in Nigeria. Excessive use could impact crop yield- the very issue herbicide use is meant to address – alongside environmental and human health issues of crops containing high herbicide residue levels.

The present study set out to address some of these concerns by replicating current field conditions in Nigeria and thus provide an insight into public health implications of herbicide use in Nigeria. They carried out the study on maize – a short duration crop that farmers grow using herbicides.

Evaluation of herbicides and metabolites

The study used a maize variety, swan-1-yellow, that is widely grown in Nigeria and planted the maize on experimental plots at the University of Port Harcourt. The maize had a popular herbicide applied at five different rates along with a plot that did not have any herbicide applied. When the maize was ripe, it was harvested and the maize evaluated for residual herbicides using chromatography – a technique commonly used to analyse plant products as discussed in the article, Blue Jacaranda Seed Oil Analysed Using Comprehensive Two Dimensional Liquid Chromatography with Quadruple Parallel Mass Spectrometry.

The study shows that when used at the correct doses, residual herbicides and their metabolites were barely detectable. But, residual levels increased with increasing dose levels. The study indicates that herbicide use by untrained and illiterate growers could be a potential health threat. The authors recommend that farmers are fully trained before using herbicides to grow crops.