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in surface waters [34].

In 2018 the European Environment Agency (EEA) indicated that chemical status of surface waters, related to pesticides, has improved between the 1st and 2nd River Basin Management Plants (RBMPs) assessments [35]. However, pesticides listed as priority substances were still detected. Among them, isoproturon and hexachlorocyclohexane were the most frequently reported, followed by endosulfan and chlorpyrifos. Furthermore, the presence of pesticides in groundwater is a failure to achieve good chemical status. As reported by EAA, several groundwater bodies exceed the permitted concentrations set by EU of total pesticides, as well as the level set for desethylatrazine, atrazine and simazine.

Herbicides such as atrazine and fungicides such as metalaxyl have been detected in aquifers for drinking water in US [25]. The most found pesticide in drinking water in Ireland was 2-methyl-4-chlorophenoxyacetic acid (MCPA), widely used for rush control in grassland [36].

      A recent study in The Netherlands, intended to assess the occurrence of pesticides in ground and surface water used as drinking water sources, has revealed the detection of 15 recently authorized pesticides, such as fluopyram and thiamethoxam, which demonstrates the importance of keeping routine monitoring methods [36].

Non-agricultural uses of pesticides are also common in urban environments, such as indoor uses or applications in gardens, roads and sealed areas, among others. As a result, triazine herbicides (atrazine, simazine and prometon) and organophosphate insecticides (chlorpyriphos and diazinon) are frequently detected in U.S. urban surface waters [34].

Pesticide occurrence in soils was inversely related to the occurrence in surface water, and one of the main factors is the hydrophobicity of the compounds, expressed by the n-octanol/water partition coefficient (K_ow). Thus, pesticides with log K_ow > 3 were more detectable in soils than in water. In a study performed in Argentine ecosystem, it was observed that the most detected herbicide residues (>30% of detection frequency) were acetochlor, atrazine and its metabolite (hydroxyatrazine), flurochloridone, glyphosate and its metabolite (aminomethylphosphonic acid, AMPA) and metolachlor, whereas the most frequently detected insecticides were chlorpyrifos and imidacloprid [37]. In this study, glyphosate and its metabolite AMPA were also found in all the environmental samples (soil, sediments and surface water), detecting AMPA up to 713 mg kg⁻¹, glyphosate at 32 mg kg⁻¹ and 5 mg l⁻¹ in sediments and water respectively.

Another group of pesticides really known for their persistence are 2,4-D-based herbicides. The two chlorine that are present in their molecules confers persistence with an estimate half-life between 7 and 312 days, which depends on the environmental conditions [38]. Several studies have reported the presence of 2,4-D and derivates in the environment because of different activities, such as agricultural activities and rain and irrigation water. Discharges from manufacturing plants, leaching and accidental spills [39] represent an important source of the aforementioned herbicide.

The key properties that determine the presence of pesticides and their accumulation in biota are hydrophobicity and persistence. Thus, if water solubility is <1 mg l⁻¹ or log K_ow is >3, they have the potential to accumulate in biota and it may be an indicator of contamination [40]. For instance, earthworms are used as indicators to the response of pesticides [41], but fish are considered as major reservoirs of pesticides and their concentration in fish tissues has been used as an indicator of bioaccumulation [42]. High concentrations of organochlorine pesticides (OCPs) have been found in fish tissues from aquatic environments in Africa [43], detecting DDTs, lindane, mirex and endosulfan at concentrations up to 100 µg kg⁻¹. Other studies, developed in South-America (southeastern Brazil and the coast of the Argentinean Pampas), showed that lindane and endosulfan levels could cause long-term or short-term damage to biota [44]. Additionally, it was observed that OCPs were highly bioaccumulated in soil mesofauna (up to 260 µg g⁻¹) [45].

In the last years, several river basins were monitored in the Iberian Peninsula, and in addition to water and sediment, biota was also analyzed. Thus, 50 pesticides were monitored in Guadalquivir river basin, but none of them were detected in biota, although there were detected in water and sediments, especially organophosphorus and triazines at concentrations up to 13 ng l⁻¹ in water and 13.2 ng g⁻¹ dry weight (dw) in sediment [46]. However, azinphos-ethyl, chlorpyriphos, diazinon, dimethoate and ethion were detected in different species of fish from Jucar river basin, observing that the maximum average concentration was found in European eels (up to 0.024 ng kg⁻¹), whereas in water, dichlofenthion, imazalil pyriproxyfen and prochloraz, commonly used in farming activities, were mainly detected [47]. In biota from Llobregat river basin, chlorpyrifos and azinphos-ethyl were detected at 44.75 ng g⁻¹ dw and 105.81 ng g⁻¹ dw, indicating possible bioaccumulation. Nevertheless, authors concluded that these values do not represent a high risk to biota. On the other hand, triazines, organophosphorus and neonicotinoids were mainly detected in water, at concentrations >600 ng l⁻¹, as can be observed in Figure 1.4, with chlorpyrifos the compound most widely detected in soils, at concentrations up to 130 ng g⁻¹ dw [48]. Additionally, the Ebro river basin was also monitored, detecting imazalil and diuron at the highest concentrations in water (410 and 150 ng l⁻¹ respectively), chlorpyrifos, diazinon and diclofenthion in sediments, whereas the only compound detected in biota was chlorpyrifos, which was detected at concentrations up to 840.2 ng g⁻¹ [49].

      Figure 1.4 Pesticide families detected in (A) water, (B) sediment and (C) fish samples from Llobregat basin in 2010 and 2011 according to the sampling point. Source [48]. Reproduced with permission of Elsevier B.V.

The presence of pesticides in air depends on the specific agricultural areas, as well as those pesticides that can be transported from nearby places, observing a relationship between the concentration of some of the compounds detected in air and diseases and mortality [50].

Several studies were performed to monitor the presence of pesticides in outdoor and indoor air [51], bearing in mind that volatile pesticides, such as OCPs, can largely remain in the atmosphere after volatilizing from contaminated soils and water. For instance, p,p’-DDT and p,p’-DDD were detected in African air at concentrations of 47 pg m⁻³ and 12 pg m⁻³ respectively, whereas other compounds as dieldrin, hexachlorobenzene (HCB), aldrin, lindane and chlordane were also detected but at lower concentrations [52].

In a study developed in Vietnam, 452 pesticides were included in a database, detecting 18 (12 insecticides, 4 herbicides and 2 fungicides) in the collected air samples, and the total concentration ranged from 3.35 to 89.0 ng m⁻³, with the most detected pesticides being permethrin, carbofuran, fenobucarb and chlorpyrifos as well as metolachlor [53]. Some prohibited pesticides in the EU, such as chlorpyrifos, permethrin, deltamethrin, cypermethrin and carbofuran, were also detected [53]. In the same country, 26 pesticides (13 pesticides, 7 fungicides and 6 herbicides) were detected in the air samples, at higher concentrations, ranging from 43 to 370 ng m⁻³. Permethrins, chlorpyrifos and propiconazole were detected and this may result from their widespread use for both agricultural and domestic purposes in rural areas [54].

Due to their high persistence, OCPs were monitored in addition to current-use pesticides (CUPs) in two National Parks in the Rio de Janeiro State. The highest concentrations of endosulfan (up to 3202 pg m⁻³), cypermethrin (881 pg m⁻³) and chlorpyrifos (270 pg m⁻³) indicated background air levels of OCPs. On the other hand, CUPs seemed to behave like pseudo-persistent organic pollutants (POPs) although it was believed that they are not persistent in the environment [55].

In another study, carbendazim, metalaxyl, myclobutanil and terbuthylazine were detected in air from rural areas of Valencia (Spain) at concentrations ranging from 16 to 174 pg m⁻³ [56].

Bearing in mind that pesticides can easily adhere to

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