Effects of pesticides on population dynamics of non-target organisms in agricultural settings: an object-oriented approach

Pesticides are chemicals that are used for pest control. They are grouped according to the type of target pests as herbicides, insecticides, fungicides, algicides, nematicides, molluscicides, etc. It is estimated that herbicides, insecticides, fungicides, and other groups of pesticides accounts for 50%, 30%, 17%, and 3% of the global pesticide use. The use of herbicides for weed control have increased the amount of food produced worldwide but also have been widely associated with the population decline of non-target organisms such as amphibians.Using an online-based survey and an object-oriented algorithm (PestTox), this study (i) surveyed how aware people in Tanzania, are of pesticides and their associated health effects, (ii) simulated fate and tranport of glyphosate and its effects on population dynamics of frogs (Crinia insignifera), and (iii) simulated the effect of spray drifts on population dynamics of frogs. Two scenarios were simulated using the width of no spray zone (buffer zone) of thirty meters and zero meters around the agricultural field for year 2012 and 2013.Results of the survey show that one hundred fifty-seven people responded to the online survey concerning the pesticide awareness. Results reveal that respondents were aware that pesticides could potentially kill them and damage the environment, yet their pesticide management practices were poor. Results suggest that poor pesticide management practices could be due to negligence. Therefore, there is a need to increase tailor-made motivational and awareness programs on best pesticide management practices.Results of the simulation modeling of fate and transport of glyphosate as well as modeling of spray drifts show that when using buffer zone width of thirty meters, spray drifts were very little compared to when using buffer zone width of zero meters. In one hundred forty-eight days after the first application, all glyphosate deposited on the crop/leaf surfaces were removed completely, suggesting that glyphosate does not stay longer on the crop/leaf surfaces. If there was no washoff events that transferred glyphosate from the crop/leaf surfaces to the topsoil, all glyphosate in the topsoil could have been removed completely by the competing processes by day forty of the simulation, implying that glyphosate does not stay longer in the topsoil.When using buffer zone width of thirty meters, glyphosate runoffs were little compared to when using buffer zone width of zero meters. This suggests that buffer zone helps to reduce the runoff of glyphosate. When using buffer zone width of thirty meters, glyphosate runoffs did not have high impact on population dynamics of frogs for year 2012 and 2013 respectively.When using buffer zone width of zero meters, the first two glyphosate runoff events for year 2013 that occurred earlier than the first glyphosate runoff event for year 2012 caused high mortality rates that killed all tadpoles within eighty-six days of the simulation, while for year 2012, all tadpoles died within one hundred five days after the first application due to high glyphosate contamination in the water body.Also, when using buffer zone width of zero meters, results of the simulation modeling of spray drifts show that no eggs were laid and the number of tadpoles, froglets, and adult frogs were very small for both year 2012 and 2013. Results suggest that high glyphosate concentration and its high toxicity could be responsible for the declining population of frogs.Results suggest that there is a need to switch to either less toxic formulations of herbicides or the use of integrated pest management tactics, or both so that herbicides may be used only when necessary, specifically, when integrated pest management tactics provide inadequate pest control.In conclusion, the algorithm presented in this study could be of practical significance to those involved in ecological and environmental modeling as well as within a management framework to evaluate potential effects of using agrochemicals in agricultural settings.