Thirty-year monitoring of s-triazine herbicide contamination in the aquifer north of Vicenza (north-east Italy).

The aquifer north of Vicenza, Italy, is one of the main and most studied drinking water reservoirs within the Veneto region. The area is an intensive cropland, and monitoring of s-triazine herbicides and metabolites has been carried out since the late eighties. This study analysed the trends of atrazine (ATR), terbuthylazine (TBZ), deethyl-atrazine (DEA), and deethyl-terbuthylazine (DET) concentrations from 1987 to 2016 and related the variations of agricultural land use, herbicide load, and pesticide regulations to the residence time of pollutants in the aquifer. In total, 785 water samples collected from 82 selected check wells were analysed with high-resolution gas chromatography combined with mass spectrometry. Non-detects were substituted by one-half the limit of detection. Over the 30 years of monitoring, concentrations of all of the pollutants decreased at all sampling sites. Since the beginning, TBZ and DET residues have been systematically lower than ATR and DEA, respectively, with more than 70% of the data below the limit of detection and never exceeding the European Maximum Acceptable Concentration (MAC) for a single pesticide (0.1 µg/L). The highest concentrations of ATR and DEA showed a spatial shift along the flow direction, suggesting an increase in groundwater residence time from the recharge zone to the accumulation zone of the aquifer. The last residues of ATR were found 27 years after its ban. Although all of the concentrations were lower than those found elsewhere in Europe, the sum of s-triazines overcame the MAC in 20% of the samples. Considering the structural and toxicological similarities of s-triazines, these findings confirm the necessity of better characterisation of the toxicological risk posed by mixtures.

Terbuthylazine contamination of the aquifer north of Vicenza (north-east Italy).

BACKGROUND AND GOAL: Agricultural practices can affect the quality of aquifers given that they are often located in cropped areas, so significant amounts of pesticides can be found in the water. In particular, triazine herbicides are always carefully checked by the official monitoring systems. The goal of this study was to find the mean concentration of terbuthylazine in an Italian aquifer and to set up a mass balance of this compound. METHODS: Terbuthylazine concentrations in the aquifer were measured in various check-wells during 1998-2004, and the value of censored data were estimated using a Gompertz inverse in order to evaluate the overall mean concentration. The total terbuthylazine load in the recharge area was calculated on the basis of surveys of cropped land and the main weed control techniques applied in the area. Data on aquifer water balance were obtained from previous studies. RESULTS AND DISCUSSION: The herbicide terbuthylazine applied in the recharge zone can be transported by surface water and enter the aquifer. Detected concentrations were always well below the EU drinking water limit and the fraction that can reach the groundwater under normal cropping practices is small, very likely less than 0.2%. RECOMMENDATIONS AND OUTLOOK: The use and application rates of pesticides should be strictly regulated in recharge areas. Vegetated buffer strips can mitigate the impact of herbicides on surface water through reducing drift and early-spring runoff. Attention should also be paid to the fate of the main metabolites from soil biochemical processes.

Time trends of 1,1,1-trichloroethane, trichloroethylene, and perchloroethylene in confined and unconfined aquifers of a groundwater system in northern Italy.

The concentrations of 1,1,1-trichloroethane, trichloroethylene, and perchloroethylene were recorded in a groundwater system of Northern Italy over the period 1985-1997. In the unconfined recharging aquifer these chemicals showed a remarkable overall decline which was accompanied by a five-fold reduction in their consumption (from approx. 250 to approx. 50 tons year-1) over the same period. The time trends for the confined aquifers indicated a steady decline for 1,1,1-trichloroethane which was accompanied by a constant concentration of trichloroethylene and an increasing presence of perchloroethylene. It is suggested that the confined aquifers are recording a contamination which took place in the unconfined recharging aquifer before monitoring period (1982) started. At present, in most of the study area 1,1,1-trichloroethane contamination is below the detection limit (0.1 microgram/L). For trichloroethylene and perchloroethylene, the average unconfined aquifer contamination accounts for approx. 1 +/- 1 and approx. 4 +/- 3 micrograms/L, respectively, while in the confined aquifers the average concentrations are approx. 8 +/- 3 and approx. 35 +/- 5 micrograms/L, respectively.