Toxicity of proton-metal mixtures in the field: linking stream macroinvertebrate species diversity to chemical speciation and bioavailability

Understanding metal and proton toxicity under field conditions requires consideration of the complex nature of chemicals in mixtures. Here, we demonstrate a novel method that relates streamwater concentrations of cationic metallic species and protons to a field ecological index of biodiversity. The model WHAM-FTOX postulates that cation binding sites of aquatic macroinvertebrates can be represented by the functional groups of natural organic matter (humic acid), as described by the Windermere Humic Aqueous Model (WHAM6), and supporting field evidence is presented. We define a toxicity function (FTOX) by summing the products: (amount of invertebrate-bound cation) (cation-specific toxicity coefficient, i). Species richness data for Ephemeroptera, Trichoptera and Plecoptera (EPT), are then described with a lower threshold of FTOX, below which all organisms are present and toxic effects are absent, and an upper threshold above which organisms are absent. Between the thresholds the number of species declines linearly with FTOX. We parameterised the model with chemistry and EPT data for low-order streamwaters affected by acid deposition and/or abandoned mines, representing a total of 412 sites across three continents. The fitting made use of quantile regression, to take into account reduced species richness caused by (unknown) factors other than cation toxicity. Parameters were derived for the four most common or abundant cations, with values of i following the sequence (increasing toxicity) H+ < Al < Zn < Cu. For waters affected mainly by H+ and Al, FTOX shows a steady decline with increasing pH, crossing the lower threshold near to pH 7. Competition effects among cations mean that toxicity due to Cu and Zn is rare at lower pH values, and occurs mostly between pH 6 and 8

Mains water leakage: Implications for phosphorus source apportionment and policy responses in catchments

Effective strategies to reduce phosphorus (P)-enrichment of aquatic ecosystems require accurate quantification of the absolute and relative importance of individual sources of P. In this paper, we quantify the potential significance of a source of P that has been neglected to date. Phosphate dosing of raw water supplies to reduce lead and copper concentrations in drinking water is a common practice globally. However, mains water leakage (MWL) potentially leads to a direct input of P into the environment, bypassing wastewater treatment. We develop a new approach to estimate the spatial distribution and time-variant flux of MWL-P, demonstrating this approach for a 30-year period within the exemplar of the River Thames catchment in the UK. Our analyses suggest that MWL-P could be equivalent to up to c.24% of the P load entering the River Thames from sewage treatment works and up to c.16% of the riverine P load derived from agricultural non-point sources. We consider a range of policy responses that could reduce MWL-P loads to the environment, including incorporating the environmental damage costs associated with P in setting targets for MWL reduction, alongside inclusion of MWL-P within catchment-wide P permits

Long-term macronutrient stoichiometry of UK ombrotrophic peatlands

In this paper we report new data on peat carbon (C), nitrogen (N) and phosphorus (P) concentrations and accumulation rates for 15 sites in the UK. Concentrations of C, N and P measured in peat from five ombrotrophic blanket mires, spanning 4000–10,000 years to present were combined with existing nutrient data from ten Scottish ombrotrophic peat bogs to provide the first UK perspective on millennial scale macronutrient concentrations in ombrotrophic peats. Long-term average C, N and P concentrations (0–1.25 m) for the UK are 54.8, 1.56 and 0.039 wt%, of similar magnitude to the few published comparable sites worldwide. The uppermost peat (0–0.2 m) is enriched in P and N (51.0, 1.86, and 0.070 wt%) relative to the deeper peat (0.5–1.25 m, 56.3, 1.39, and 0.027 wt%). Long-term average (whole core) accumulation rates of C, N and P are 25.3 ± 2.2 gC m− 2 year−1 (mean ± SE), 0.70 ± 0.09 gN m− 2 year− 1 and 0.018 ± 0.004 gP m− 2 year− 1, again similar to values reported elsewhere in the world. The two most significant findings are: 1) that a regression model of N concentration on P concentration and mean annual precipitation, based on global meta data for surface peat samples, can explain 54% of variance in N concentration in these UK peat profiles; and 2) budget calculations for the UK peat cores yield an estimate for long-term average N-fixation of 0.8 g m− 2 year− 1. Our UK results, and comparison with others sites, corroborate published estimates of N storage in northern boreal peatlands through the Holocene as ranging between 8 and 15 Pg N. However, the observed correlation of N% with both mean annual precipitation and P concentration allows a potential bias in global estimates that do not take this into account. The peat sampling data set has been deposited at the NERC Data Centre (Toberman et al., 2016)

Structure Activity Relationships of α_v Integrin Antagonists for Pulmonary Fibrosis by Variation in Aryl Substituents

Antagonism of α_vβ₆ is emerging as a potential treatment of idiopathic pulmonary fibrosis based on strong target validation. Starting from an α_vβ₃ antagonist lead and through simple variation in the nature and position of the aryl substituent, the discovery of compounds with improved α_vβ₆ activity is described. The compounds also have physicochemical properties commensurate with oral bioavailability and are high quality starting points for a drug discovery program. Compounds <b>33S</b> and <b>43E1</b> are pan α_v antagonists having <i>ca.</i> 100 nM potency against α_vβ_3, α_vβ_5, α_vβ₆, and α_vβ₈ in cell adhesion assays. Detailed structure activity relationships with these integrins are described which also reveal substituents providing partial selectivity (defined as at least a 0.7 log difference in pIC₅₀ values between the integrins in question) for α_vβ₃ and α_vβ₅