Abstract:
Aquatic environments, while not the target of many pesticide applications, often receive chemicals
through catchment runoff dynamics. In this regard, the use of pesticides in agricultural systems
may have deleterious effects on aquatic ecosystems within the same catchment area. Here using a
series of in–situ and ex–situ experiments, the study assessed (a) pesticide concentrations of
acetamiprid and chlorpyrifos across MACADAMIA ORCHARD and communal area reservoirs
using liquid chromatography tandem mass spectrometry (LC–MS/MS), (b) the behavioural
responses of Mozambique tilapia, Oreochromis mossambicus, following exposure to three
commonly used macadamia pesticides (i.e., Karate Zeon 10 CS, Mulan 20 SP, Pyrinex 250 CS at
different concentrations, (c) macadamia Macadamia integrifolia leaf litter decomposition and
mosquito colonisation following pesticide exposure, and (d) macroinvertebrate colonisation
associated with introduced stone substrates in cages within the MACADAMIA ORCHARD and
control reservoirs to explore whether macadamia pesticides affected on macroinvertebrate
colonisation dynamics.
Firstly, analysis of acetamiprid and chlorpyrifos associated with sediments in MACADAMIA
ORCHARD reservoirs revealed mean pesticide concentrations of 14.48 μg L–1 and 5.67 μg L–1,
respectively, whereas, in communal area reservoirs outside of agricultural catchments, both
pesticides were not detected. Acetamiprid was not detected across reservoir water, whereas the
mean pesticide concentration of chlorpyrifos of 6.51 μg L–1 (MACADAMIA ORCHARD) and
0.13 μg L–1 (communal area) were detected. Secondly, O. mossambicus demonstrated different
onset behavioural responses, i.e., swimming erratically, surfacing, vertical positioning, loss of
equilibrium, being motionless and mortality with high mortality at increased mortality. Thirdly,
macadamia leaf litter tended to decompose faster when exposed to pesticide treatments, whereas
chlorophyll–a were reduced. Furthermore, pesticide treatments seemed to promote mosquito (i.e.,
Culex spp.) and pupal abundances. Finally, a total of 644 macroinvertebrate individuals were
recorded across macadamia and communal reservoirs, mostly dominated by Chironominae (55.1
%), Ostracoda (14.4 %), Trithemis sp. (5.2 %), Anax sp. (5.2 %) and Radix natalensis (5.0 %).
The results indicate that MACADAMIA ORCHARD reservoirs are highly contaminated by
acetamiprid and chlorpyrifos and that these contaminants have implications for the ecological
functioning of aquatic ecosystems. Reduction of species diversity adjusted community structure
and altered energy flow and nutrient recycling were all demonstrated. The results of the study
collectively show how common pesticides used in the macadamia plantation may be exert pressure
on adjacent freshwater ecosystems. Future studies should examine effects on trophic interactions,
pesticide accumulation in faunal groups and allochthonous trophic transfer dynamics to terrestrial
environments. Such information would be useful for managers tasked with mitigation plans for the
region.
