## 3 Results and Discussion
### Pesticide Residues in Apples and Citrus Fruits--Comparison
#### 3.1.2 Citrus Fruits
Their average concentrations in grapefruit, lemon, orange and mandarin exceeded the maximum residue limit (MRL) values. In some of the fruits, several other pesticides, e.g., bensulphuron methyl and demeton-S-methyl-sulphoxide, were noted at levels above the MRL. In a study by [PERSON] et al. [77], pesticide residues were detected in 31 out of 200 (15.5%) samples of fruits (oranges, grapefruit, lemons, mandarins, peaches, pears, grapes) and vegetables (tomato, potato). In fruit samples, pesticide residues were found in 22 out of 120 (18.3%) analysed samples. Imazalil was identified in 18 samples (range of 0.020-4.1 mg/kg). Chlorpyrifos was detected in eight samples at concentrations from 0.030 mg/kg to 0.27 mg/kg, and foran in three samples, at low concentrations ranging from 0.011 mg/kg to 0.019 mg/kg. In a single sample, ethion was detected at a concentration of 0.27 mg/kg. Imazalil constituted the highest percentage (66.6%) of pesticides identified in the analysed fruits. In eight samples of fruits, pesticide residues exceeded the MRL values and were classified as hazardous if used for human consumption. Figure 6 presents the frequency of occurrence of pesticides in the analysed samples of citrus fruit flesh, expressed in the form of percentage share of burdened samples. In 2012 and in 2020, in all analysed samples of citrus fruits, the presence of the fungicide imazalil was detected. The second most frequent pesticide in the analysed samples of citrus fruits was the fungicide pyrimethanil, whose residues were detected in 50% of the analysed samples in the years of the study. Imazalil and pyrimethanil are fungicides extensively used in agriculture, especially in the cultivation of citrus fruits. They provide surface protection of fruits, especially citrus fruits, against the growth of moulds on their surface. Unfortunately, analyses on the flesh of fruits protectively coated with those compounds prove that the fungicides penetrate into the fruits [75; 76]. Comparing the results concerning the content of pesticide residues in apples and in citrus fruits, one can note that apples were characterised by a significantly greater diversity of identified pesticides, i.e., 27 and 8 identified compounds in apples, and only 4 pesticides in citrus fruits. According to the Report of the Ministry of Health [70] in Poland in 2017, no instances of exceeded values of MRL in analysed samples of oranges were observed. No pesticide residues were found in 7% of the analysed samples [70]. In 93% of the analysed oranges, the presence of at least one pesticide was detected. In 80% of the samples, the presence of at least two pesticides was noted. None of the samples of oranges contained residues of more than nine identified pesticides. The most often identified pesticides were the following: imazalil (91% of the samples, with average concentration of 0.603 mg/kg), thiabendazole (48% of the samples, with average concentration of 0.380 mg/kg), chlorpyrrifos (41% of the samples, with average concentration of 0.023 mg/kg), pyrimethanil (34% of the samples, with average concentration of 0.267 mg/kg), 2.4-D (30% of the samples, with average concentration of 0.030 mg/kg) and 2-phenylphenol (29% of the samples, with average concentration of 0.212 mg/kg), as well as carbendazim (16% of the samples), dithiocarbamates (14% of the samples), propiconazole (14% of the samples), buprofezin (13% of the samples), azoxystrobin (11% of the samples), pyraclostrobin (11% of the samples) and chlorpyrrifos methyl (9%) [70]. Imazalil is a fungicide which is used mainly after the harvest, which means that it should be found on the peel of orange fruits [80]. A study conducted by Swiss researchers on citrus fruits demonstrated that imazalil was detected in 70% of cases [81]. Chlorpyrrifos was identified in eight samples at concentrations from 0.030 mg/kg to 0.27 mg/kg. Chlorpyrrifos is an organophosphate insecticide extensively used in agriculture.