Establishing the extent of pesticide contamination in Irish agricultural soils

Abstract

To establish meaningful and sustainable policy directives for sustainable pesticide use in agriculture, baseline knowledge of pesticide levels in soils is required. To address this, five pesticides and one metabolite widely used in Irish agriculture and five neonicotinoid compounds pesticides were screened from soils from 25 fields. These sites represented a diversity of soil and land use types. Prothioconazole was detected in 16 of the 18 sites where it had been recently applied, with the highest maximum concentration quantified of 46 μg/kg. However, a week after application only four fields had prothioconazole concentrations above the limit of quantification (LOQ). Fluroxypyr was applied in 11 sites but was not detected above LOQ. Glyphosate and AMPA were not detected. Interestingly, neonicotinoids were detected in 96% of all sampling sites, even though they were not reported as recently applied. Excluding neonicotinoids, 60% of sites were found to contain pesticide residues of compounds that were not previously applied, with boscalid and azoxystrobin detected in 15 of the 25 sites sampled. The total number of pesticides detected in Irish soils were significantly negatively correlated with clay fraction, while average pesticide concentrations were significantly positively correlated with log K_ow values. 17 fields were found to have total pesticide concentrations in excess of 0.5 μg/kg, even when recently applied pesticides were removed from calculations. Theoretical consideration of quantified pesticides determined that azoxystrobin has high leaching risk, while boscalid, which was detected but not applied, has an accumulation risk. This information provides insight into the current level of pesticide contamination in Irish agricultural soil and contributes to the European-level effort to understand potential impacts of pesticide contamination in soil.

Keywords: Irish agricultural soil; Monitoring; Neonicotinoids; Pesticide residues; Risk assessment.

Graphical abstract

Fig. 1

Sampling point map of the research area (Republic of Ireland), callouts are for the counties Kildare (top) and Kilkenny (bottom). The label for each point indicates the field's label: EGL: Extensive grassland.; IGL: Intensive grassland.; CL: Cropland.; CA: Commonage Area.

Fig. 2

Applications and levels of detection for the different pesticide types investigated in this study.

Fig. 3

Distribution of quantified pesticides in Irish agricultural soils (a) studied fields based on the number of multi-residues (b) pesticide detection frequency and concentration.

Fig. 4

Hierarchical cluster heatmap analysis of nine detected pesticides clustered by concentration profiles of targeted pesticides and sampling site details. The colour of each cell represents the log₁₀ pesticide concentrations. The dendrogram was cut to present two clusters of sample sites and two clusters of targeted pesticides. Notation. EGL = Extensive grassland; IGL = Intensive grassland; CL = Cropland; CA = Commonage area.

Fig. 5

Simplified hierarchical cluster analysis heatmap clustered by log₁₀ concentration profile (a) Crop types clustered by pesticide types (b) Crop types clustered by targeted pesticides (excluding neonicotinoid).

Fig. 6

Pearson correlations coefficient plot based on the number of soils containing quantifiable pesticide residues (n = 24): (a) the total number of pesticide content is represented with the measured soil properties, (b) The frequency of pesticide detection and pesticide average concentrations correlated with their pesticide properties. Notation. SM = Soil Moisture; SWHC = Soil Water Holding Capacity; SOM = Soil Organic matter; TP = Total Phosphorus; TN = Total Nitrogen; TNPD = Total Number of Pesticides Detected; Vp = Vapour pressure; DT₅₀ = Half-life; WS = Water Solubility; GUS = Groundwater Ubiquity Score; Freq = Frequency of detection; Avg = Average concentration “N”.

Fig. 7

Fluctuation of the total concentration of individual pesticide analytes compared within 24 h and one week after pesticide application (n = 13), (a) all the targeted pesticides except prothioconazole, and (b) prothioconazole. Notation. Ace = Acetamiprid; Azo = Azoxystrobin; Bos = Boscalid; Cloth = Clothianidin; Flu = Fluroxypyr; Imi = Imidacloprid; Pro = Prothioconazole; Thiac = Thiacloprid; Thiam = Thiamethoxam; 24 h = within 24 h of pesticide application; and 1 w = after 1 week of pesticide application. The error bars represent SD.

Fig. 8

Pesticide concentrations at a field level, considering (a) total pesticide quantified and (b) pesticides that were detected but not applied (n = 25).

Fig. 9

Field level total pesticide concentration of widely used pesticides within 24 h and one week after pesticide application (n = 13).