Abstract
The spatial distribution of antibiotics in alluvial aquifers presents a large variability caused by the joint action of several factors including hydrology, land use, and groundwater properties. In this study, the influences of these factors on the spatial variability of antibiotics is evaluated based on an extensive database of 47 wells located in the Baix Fluvià alluvial aquifer (NE Catalonia). Statistical methods such as redundancy and variation partitioning (VP) analyses, which are not commonly used in hydrogeological studies, are herein tested and used to estimate the effects of environmental factors on the observed antibiotic occurrence. Using VP, the total explained variation of the antibiotic distribution only reaches 18% of the total variability, meaning that the whole set of explanatory parameters is insufficient or inadequate to describe the occurrence of antibiotics and their concentration. The results point out that groundwater properties are the most representative parameters, while those related to antibiotic sources and aquifer susceptibility have lower influences. Omitting solute transport parameters that actually govern antibiotic fate (i.e., sorption coefficients and degradation rates) from the statistical analysis limited the success of the VP results. VP thus highlights the importance of researching antibiotic transport in groundwater by determining the reactive properties of these pollutants above other hydrogeochemical variables. We conclude that the present capacity to predict antibiotic existence at a specific location—for instance, a supply well—based on field data is still poor and unrepresentative, being an impediment for groundwater pollution management.
Highlights
The occurrence and distribution of contaminants of emerging concern (CECs) at a regional scale presents a large spatial variability attributed to the joint action of several factors, including hydrology and land use as well as transport processes occurring in the soil zone and later in the aquifer [1,2,3,4,5]
The antibiotic dataset indicates that just a few (11) of the 53 analyzed antibiotics were found in groundwater samples, with ciprofloxacin and sulfamethoxazole having larger detected concentrations (21 and 36 among the 47 sampled wells, respectively; Figure 2)
Enrofloxacin, and sulfamethoxazole were widely identified in the Fluvià River samples, appearing at higher concentrations than those found in groundwater (Figure 2)
Summary
The occurrence and distribution of contaminants of emerging concern (CECs) at a regional scale presents a large spatial variability attributed to the joint action of several factors, including hydrology and land use as well as transport processes occurring in the soil zone and later in the aquifer [1,2,3,4,5]. Antibiotics are related to the urban water cycle as well as to fertilization practices using husbandry slurry and manure, and they are usually present in alluvial aquifers (e.g., reference [9]). Their main input sources are stream recharge, which carries the pollutant load from wastewater treatment plants, and direct infiltration from rainfall, which leachates veterinary pharmaceuticals associated with organic fertilizers. Researchers and managers still lack a broad perspective to propose effective (in effort and cost) monitoring strategies to assess this type of pollution
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