Paul Kojo Mensah, a SSAWRN student at Rhodes University in South Africa, has tackled and completed a project of great value and considerable complexity: testing the effects of herbicide use on aquatic organisms in the Eastern Cape region, and developing guidelines for herbicide use based on the responses of those organisms.
Paul's interest in this topic grew out of his discovery that there were no such local guidelines in place, and considerable reason for concern, given the increasing use of herbicides by farmers, private land owners, public agencies, and the flourishing wine industry.
Paul, who was born in Ghana, has always dreamed of using his biological training to help protect the environment. When he was studying biology as an undergraduate at the University of Cape Coast in his home country, he hoped to move on to graduate school so that he could become a marine biologist and a university professor. After graduating with honors in 2001, however, he was unable to find sponsorship for his master's studies - like most other science graduates in Africa. He had no choice but to enter the job market, and was fortunate to find work teaching in a secondary school in Ghana.
After four relatively unproductive years, he moved to South Africa in 2005 to try his luck in a new environment. Again, he supported himself by teaching in secondary school, enrolling at the same time in the new Walter Sisulu University in the Eastern Cape, recently formed by a merger of three other institutions. He saved as much money as he could from his teaching salary, and by 2006 was able to begin his MSc studies in zoology, working also as a teaching assistant at the university.
By 2008, he had completed his MSc and began trying to find a supervisor and support for PhD studies in ecotoxicology, an interest he had acquired at WSU. While searching the Web, he came across the name of Dr. Nikite Muller at Rhodes University's Institute for Water Research in Grahamstown. He emailed her, and she suggested that he apply to the RISE program as well as to Rhodes. In November 2008 he received an emailed acceptance from both programs.
Working with Dr. Muller and her colleague Prof. Tally Palmer, both members of the Institute for Water Research (IWR) at Rhodes, he had access to many potential research ideas. He would not be working in marine biology, as he had earlier planned, but he soon learned that he might be able to make a substantial contribution in freshwater biology. He heard about a problem that was receiving virtually no research attention in South Africa - the growing presence of toxic chemicals in waterways and the effects of these chemicals on aquatic organisms. Both of his mentors, who had long experience in the field of ecotoxicology, encouraged his interest and helped guide his research planning.
As he learned about the regional use of herbicides to control weeds and invading aquatic species, he was not surprised to find that the most widely used chemical was glyphosate, most commonly sold under the commercial name Roundup and liberally used throughout the province. He was surprised, however, to find that South Africa had no water quality guidelines for glyphosate that were based on indigenous species, unlike the United States, Australia, Canada, and the European Community - even though it has been found in high concentrations since the 1990s in the Hex River Valley, an intensive grape-farming area in the Western Cape Province.
There were reasons for urgency in creating science-based guidelines. One is that glyphosate is commonly used near and even on rivers and other waterways, draining into them when it rains. As an aquatic biologist, Paul knew that many species of aquatic animals are sensitive to chemical pollutants, and he saw the need to protect populations of economic and ecological value. Also, he learned that weed species in South Africa and elsewhere are quickly developing resistance to glyphosate, prompting some users to increase their application rates.
The action of glyphosate was discovered in 1970 by John Franz, an American chemist employed by Monsanto, and glyphosate was introduced commercially in 1974. Franz and his team discovered that the glyphosate molecule interferes with an enzyme vital to a critical biochemical pathway in virtually every plant, bringing farmers a powerful new tool in their war with weeds. And unlike its predecessors DDT and 2,4-D, glyphosate seemed to bring little or no risk to humans or other animals, in which this pathway is not present. For many years before Paul began his work, glyphosate was viewed by many agricultural researchers as the "perfect herbicide" - a broad-spectrum, systemic agent that killed virtually every weed and invasive species, broke down in the environment, and posed little risk to users.
Over the next two decades, glyphosate's popularity grew steadily but slowly. Farmers used it to spray fields before planting, but they could not use it after crops emerged. In 1996, however, this all changed when molecular geneticists succeeded in moving a glyphosate-resistant gene from a soil bacterium into ordinary crops. This meant that every major "world crop," from corn to rice to wheat, could be shielded from the danger of glyphosate, which could now be applied directly to the crops themselves and the weeds among them. Monsanto developed seeds for these resistant strains and watched the use of glyphosate soar around the world. Within a decade, some 90 percent of all major crops were grown with the Roundup Ready system, which included both the spray and the seeds. From then until now, about half of Monsanto's revenues have been generated by this system.
Recently, however, the Roundup picture has clouded somewhat. Persistent use of glyphosate has spurred the emergence of resistant weed strains, including some "superweeds" that dominate as the weeds around them succumb. And evidence is accumulating that the Roundup system is not quite as safe as it was thought to be. Numerous studies have found evidence that it does indeed harm some organisms, such as the nitrogen-fixing bacteria in soil and many species of frogs, which are commonly viewed as the aquatic equivalent of "the canary in the coal mine."
While the glyphosate molecule itself is thought to be safe, it must be mixed with "adjuvant" chemicals, such as surfactants, that enhance its application or activity. It is these glyphosate formulations that appear to threaten some animals, often through changes in reproductive, endocrine, nerve, or developmental functions. Studies have also suggested that the formulations can alter the natural biota and nutrient availability of soil and damage human DNA, among other effects.
These assertions are disputed by Monsanto, and the heavy application of glyphosate has continued in regions worldwide, including the Eastern Cape. Paul's primary objective has been to evaluate its safety and to design evidence-based guidelines for use. In order to gain perspective for his work he began by examining other countries' guidelines. Then he began testing the sensitivity of local aquatic organisms.
Many of them showed some degree of sensitivity to glyphosate exposure, but he began by looking for a single reliable biomarker, or indicator species, that was both common and sensitive to herbicides. Through the IWR, he worked closely with the Department of Water Affairs at sites along the Swartkops River to plan his research strategy. He found what he needed in Caridina nilotica, a common fresh-water shrimp occurring throughout the continent, from the Nile to South Africa. He found that this shrimp is both sensitive to herbicide pollution and exhibits a range of responses that can be readily observed.
One was that Roundup depressed the activity of a vital enzyme, acetylcholine esterase (AChE); the higher the concentration of herbicide, the greater the depression of AChE activity. AChE is essential to the transmission of nerve signals, especially at nerve-muscle junctions and in the brain.
A second behavior of C. nilotica caused by glyphosate was lipid peroxidation (LPx), a process which results in the degradation of the fats in cell membranes. Paul tested this behavior by exposing post-hatch shrimps to high concentrations of Roundup for 96 hours to measure acute toxicity; he also exposed them to smaller amounts of herbicide over a much longer 21-day period. Biochemical testing showed that LPx was significantly higher in animals exposed to Roundup than in control animals.
Finally, he assessed the toxicity of Roundup using three different life stages of the shrimp: neonates (less than seven days after hatching), juvenile (more than seven days and fewer than 20 days post-hatching), and adult (more than 40 days post-hatching). All were exposed to varying concentrations of the herbicide in 48- and 96-hour tests. All three life-stages of the shrimps that were exposed to herbicide responded with erratic and slow movements, with neonates showing the most irregular behavior. This indicated that even low levels of Roundup may adversely affect the health and survival of C. nilotica.
For his ultimate goal of suggesting guidelines for both short-term and long-term exposure to glyphosate, Paul chose to examine the responses of eight species of organisms belonging to five taxonomic groups: insects, crustaceans, mollusks, fish, and green algae. He measured the effects of both high-level, acute exposure, such as might be caused by spills and surface runoff, and to low-level, chronic exposure, as might be caused by gradual, steady seepage of herbicide from soil into nearby waterways.
He found wide variations in sensitivity among the test species. For example, the water flea, Daphne pulex, was about nine times more sensitive to glyphosate than the midge, Tanytarsus flumineus. For the algal species, Chlorella sorokiniana was found to be 10 times more sensitive in a 48-hour exposure than C. protothecoides, and 200 times more sensitive in a 72-hour exposure. Arthropods and fish were the least sensitive of the groups tested. Based on analysis of his data on species sensitivity, he was able to recommend water quality guidelines that can help avoid both severe effects during acute, transient events (such as spills) and long-term exposure. In general, he concluded that the herbicide should be carefully managed to minimize any negative impact on non-target freshwater organisms, and suggested the amount of herbicide that can be used safely. To date, Paul and his co-authors have published four papers on these results. He based his PhD thesis on this work, and it has been successfully completed.
Meanwhile, Paul's circle of connections in the world of freshwater management has expanded with the departure of Dr. Muller from Rhodes University. She left in 2010 to become an environmental officer with Amatola Water, a water services provider to municipalities in the Eastern Cape. She remains his co-supervisor, along with Prof. Palmer.
He now hopes to continue his study of the herbicide as a postdoctoral fellow if he is able to find support for his work. Much remains to be done, as the use of glyphosate in the Eastern Cape continues to be heavy. The provincial government has been cooperating with Monsanto since 2005, when the company began providing farmers with GM seed and the Roundup regimen. "One result is that the farmers are using too much Roundup," said Paul. "They believe that 'If some is good, more is better.' They are also using more no-till farming, which requires lots of herbicide. Ours is still the only field work being conducted on this issue, and we have the responsibility to communicate what we have found."