toxicity - pesticides, herbicides and insecticides - Blackherbals.com

Continued from page 67 – South Africa: DevelopingGuidelines for 'Roundup' in South Africafixing bacteria in soil and many species of frogs, whichare commonly viewed as the aquatic equivalent of "thecanary in the coal mine."While the glyphosate molecule itself is thought to besafe, it must be mixed with "adjuvant" chemicals, suchas surfactants, that enhance its application or activity. Itis these glyphosate formulations that appear to threatensome animals, often through changes in reproductive,endocrine, nerve, or developmental functions. Studieshave also suggested that the formulations can alter thenatural biota and nutrient availability of soil anddamage human DNA, among other effects.These assertions are disputed by Monsanto, and theheavy application of glyphosate has continued inregions worldwide, including the Eastern Cape. Paul'sprimary objective has been to evaluate its safety and todesign evidence-based guidelines for use. In order togain perspective for his work he began by examiningother countries' guidelines. Then he began testing thesensitivity of local aquatic organisms.Many of them showed some degree of sensitivity toglyphosate exposure, but he began by looking for asingle reliable biomarker, or indicator species, that wasboth common and sensitive to herbicides. Through theIWR, he worked closely with the Department of WaterAffairs at sites along the Swartkops River to plan hisresearch strategy. He found what he needed in Caridinanilotica, a common fresh-water shrimp occurringthroughout the continent, from the Nile to South Africa.He found that this shrimp is both sensitive to herbicidepollution and exhibits a range of responses that can bereadily observed.One was that Roundup depressed the activity of a vitalenzyme, acetylcholine esterase (AChE); the higher theconcentration of herbicide, the greater the depression ofAChE activity. AChE is essential to the transmission ofnerve signals, especially at nerve-muscle junctions andin the brain.A second behavior of C. nilotica caused by glyphosatewas lipid peroxidation (LPx), a process which results inthe degradation of the fats in cell membranes. Paultested this behavior by exposing post-hatch shrimps tohigh concentrations of Roundup for 96 hours to measureacute toxicity; he also exposed them to smaller amountsof herbicide over a much longer 21-day period.Biochemical testing showed that LPx was significantlyhigher in animals exposed to Roundup than in controlanimals.Finally, he assessed the toxicity of Roundup using threedifferent life stages of the shrimp: neonates (less thanseven days after hatching), juvenile (more than sevendays and fewer than 20 days post-hatching), and adult(more than 40 days post-hatching). All were exposed tovarying concentrations of the herbicide in 48- and 96-hour tests. All three life-stages of the shrimps that wereexposed to herbicide responded with erratic and slowmovements, with neonates showing the most irregularbehavior. This indicated that even low levels of Roundupmay adversely affect the health and survival of C.nilotica.For his ultimate goal of suggesting guidelines for bothshort-term and long-term exposure to glyphosate, Paulchose to examine the responses of eight species oforganisms belonging to five taxonomic groups: insects,crustaceans, mollusks, fish, and green algae. Hemeasured the effects of both high-level, acute exposure,such as might be caused by spills and surface runoff, andto low-level, chronic exposure, as might be caused bygradual, steady seepage of herbicide from soil intonearby waterways.He found wide variations in sensitivity among the testspecies. For example, the water flea, Daphne pulex, wasabout nine times more sensitive to glyphosate than themidge, Tanytarsus flumineus. For the algal species,Chlorella sorokiniana was found to be 10 times moresensitive 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 thegroups tested. Based on analysis of his data on speciessensitivity, he was able to recommend water qualityguidelines that can help avoid both severe effects duringacute, transient events (such as spills) and long-termexposure. In general, he concluded that the herbicideshould be carefully managed to minimize any negativeimpact on non-target freshwater organisms, andsuggested the amount of herbicide that can be usedsafely. To date, Paul and his co-authors have publishedfour papers on these results. He based his PhD thesis onthis work, and it has been successfully completed.Meanwhile, Paul's circle of connections in the world offreshwater management has expanded with the departureof Dr. Muller from Rhodes University. She left in 2010to become an environmental officer with Amatola Water,a water services provider to municipalities in the EasternCape. She remains his co-supervisor, along with Prof.Palmer.He now hopes to continue his study of the herbicide as apostdoctoral fellow if he is able to find support for hisContinued on page 6969-- Traditional African Clinic July 2013