Southern Cross University performed soil and sediment quality investigations on farms with
various land use histories, including blueberry and banana cultivation, with funding from the
Coffs Harbour City Council’s Environmental Levy program.
Terrestrial soils from chemical mixing sheds, crop production areas (fields), drainage areas,
and bottom sediments from retention reservoirs (dams) were sampled from three different
sites in the Coffs Harbour local government area. Sites 1 and 2 were in the Sandy Beach
catchment, while Site 3 was in the Bucca Bucca Creek catchment. All three sites are currently
used for blueberry cultivation.
Terrestrial soil cores were analysed for 97 different pesticide residues of different classes
(herbicides, insecticides, fungicides). Additionally, terrestrial soil and dam sediment cores
were analysed for trace metal contents.
Spatial distributions of pesticides and trace metals in terrestrial soils and sediments were
analysed to identify contaminated sites. Comparisons to the Australia and New Zealand
Environment and Conservation Council (ANZECC) and other soil quality guidelines (SQG)
and enrichment factors (anthropogenic vs. naturally occurring portions) were used to assess
contamination of trace metals.
The farm in the Bucca Bucca catchment (Site 3) had the greatest degree of contamination
with pesticides. Fifty percent of the detectable pesticide residues were from two cores at this
site. Ninety-eight percent of the total detected pesticide mass was observed in the chemical
mixing shed core from Site 3. The fungicides propiconazole and cyprodinil were the most
abundant pesticides from this core. Soil contents of these fungicides should decline as they
degrade via natural processes, however propiconazole and cyprodinil can persist in the
environment while bound to soil organic material. Degradation rates remain uncertain.
Additionally, toxicity of propiconazole and cyprodinil degradation products may be greater
than their parent compounds.
14 of 26 subsamples of terrestrial soil and dam sediment cores from Site 2 in Sandy Beach
had arsenic contents over the SQG low value (20 mg kg-1). One of these samples exceeded
the SQG high range value (70 mg kg-1). Arsenic is suspected to be from pesticide application
which occurred during previous land use (banana cultivation).
Subsamples from dam sediment cores at all three sites had mercury (Hg) contents over the
SQG low value (150 μg kg-1). Mean contents of Hg from dam sediments (141 ± 15.5 μg kg-1)
were greater than terrestrial soils (78 ± 6.5 μg kg-1) suggesting mobility of Hg from terrestrial
soils and retention in nearby sediments.
Overall, based on their environmental toxicity, distribution, persistence, and mobility we
identified the herbicide diuron, trace metals cadmium (Cd) and (Hg), and the fertiliser
nutrient phosphorus (P) as contaminants of high concern. Using international pesticide
toxicity standards from the Globally Harmonised System of classification and labelling of
chemicals, we classified all other detected pesticides as contaminants of potential concern.
We highlight that our sampling was spatially restricted and suggest more sampling of farm
soils to increase confidence in identifying contaminants of concern.