Long-term leaching through clayey till of N,N-dimethylsulfamide, a Persistent and Mobile Organic Compound (PMOC).

Environmental pollution with Persistent and Mobile Organic Compounds (PMOC) from anthropogenic activities is an increasing cause for concern. These compounds are readily leached to groundwater aquifers and are likely to resist degradation, putting pressure on groundwater resources. Pesticides can form PMOCs upon degradation in the environment. The PMOC N,N-dimethylsulfamide (DMS) was the most frequently detected pesticide metabolite in Danish drinking water wells in 2020, although the pesticidal use of the last parent compound (tolylfluanid) ended in 2007. This study aimed to improve the understanding of the leaching of the PMOC DMS from clayey tills by combining a review of compound properties, sources and use, comprehensive field observations and numerical flow and solute transport modeling. The modeling explored the mechanisms of DMS retention during vertical transport in clayey till and the fingerprint in the underlying aquifer. The results were supported by detailed field observations at an agricultural site with strawberry production. Porewater samples were collected from clayey till to a depth of 12 m bgs by a custom designed installation method of suction cups. Groundwater sampling (249 samples) was designed to provide vertical concentration profiles at various distances from the presumed sources. The review of properties showed that the parent compounds and intermediates degrade quickly in topsoil, releasing the highly persistent and mobile DMS. We tested the effect of fractures on transport with different hydraulic apertures and a scenario without fractures by numerical modeling. The results showed that the presence of fractures can smooth the breakthrough curve below the clayey till, leading to faster breakthrough, lower maximum concentration, and several decades of prolonged leaching in simulations with the largest aperture (20 µm). The fracture-matrix interaction is a possible explanation for the observed delay of leaching from clayey till. The vertical concentration profiles in groundwater were used for identifying the sources at the field site and testing source strengths. Assigning one point source (200 µg/L) and two diffuse sources (40-50 µg/L) to the model produced vertical concentration profiles that compared well with observed field data in clayey till and the aquifer. All results were integrated into a conceptual model for the environmental fate of PMOCs in soil and groundwater. The findings of this study imply that the presence of fractures in clayey till should be considered in conceptual site models, since they can substantially prolong the leaching of PMOCs to groundwater. The integration of comprehensive field investigations and numerical modeling is key to understand the fate of PMOCs in complex field systems with different source types. Together with widespread occurrences of PMOCs in groundwater systems, the results highlight the need for improved approval procedures for pesticides and biocides which considers their persistent and mobile metabolites.

Cross-reactivity between methylisothiazolinone, octylisothiazolinone and benzisothiazolinone using a modified local lymph node assay.

BACKGROUND: In the light of the exceptionally high rates of contact allergy to the preservative methylisothiazolinone (MI), information about cross-reactivity between MI, octylisothiazolinone (OIT) and benzisothiazolinone (BIT) is needed. OBJECTIVES: To study cross-reactivity between MI and OIT, and between MI and BIT. METHODS: Immune responses to MI, OIT and BIT were studied in vehicle and MI-sensitized female CBA mice by a modified local lymph node assay. The inflammatory response was measured by ear thickness, cell proliferation of CD4+ and CD8+ T cells, and CD19+ B cells in the auricular draining lymph nodes. RESULTS: MI induced significant, strong, concentration-dependent immune responses in the draining lymph nodes following a sensitization phase of three consecutive days. Groups of MI-sensitized mice were challenged on day 23 with 0·4% MI, 0·7% OIT and 1·9% BIT - concentrations corresponding to their individual EC3 values. No statistically significant difference in proliferation of CD4+ and CD8+ T cells was observed between mice challenged with MI compared with mice challenged with BIT and OIT. CONCLUSIONS: The data indicate cross-reactivity between MI, OIT and BIT, when the potency of the chemical was taken into account in choice of challenge concentration. This means that MI-sensitized individuals may react to OIT and BIT if exposed to sufficient concentrations.