Proposal for estimation of surface water bodies background levels for selected metals Slovak Republic

State Geological Institute of Dionýz Štúr, Bratislava ________________________________________________________________ Slovak Hydrometeorological Institute, Bratislava Slovak Water Management Authority Institute of Hydrology SAS, Bratislava Water Research Institute, Bratislava

Background level means the concentration of a substance or the value of an indicator in a body of surface water corresponding to no, or only very minor, anthropogenic alterations to undisturbed conditions. The estimation of background levels for single chemicals in groundwater is rather complicated and also „sensitive“ dilemma not only from the scientific but also from the economic point of view (implementation of WFD, river basin management plans, measures etc.). The proposed methodology of their estimation stems from the feasibility of the input information, conceptual model and scientifically review of results in specific natural conditions of Slovak Republic.

Estimatimation of the BL – statistical approach oDetermination of the character of the distribution of evaluated chemical element / compound (visually, histogram, testing of character of distribution) oCensored data < 40% values below LOQ - substitution method (LOQ/2) 40% - 60% values below LOQ - Kaplan-Meier´s analysis > 60% values below LOQ - meaningful value (LOQ) oCalculation of background value (identification and elimination of outliers). This step is individual for each element / compound and is managed by the character of the input data. After optimization (2σ-technic, trimmed mean, x + 2σ) we recommend to use median + 2*(Median Absolute Deviation)

Median Absolute Deviation (MAD) 1.Resistant estimator of spread (statistical point of view) 2.Suitable for geogenic and anthropogenic anomalies detection (geochemical point of view) The MAD is computed by first listing the absolute value of all differences |d| between each observation and the median. The median of these absolute values is than MAD. MAD (X i ) = median |d i |, where d i = X i – median |X i | BL = median + 2*MAD

Input data for estimation of the background levels in surface water bodies Components for background levels estimation: –selection followed EU and Slovak legislation – mainly priority and dangerous substances –Cd, Hg, As, Pb, Ni, Cr, Zn, Cu and Al (other under preparation) Analytical results from the national geochemical mapping programme (statistical sampling density: 1 sample/ 4 sqr km – samples of surface water – not the whole Slovak territory covered) Surface water quality monitoring network (time factor, regime variability) – samples from time period 1995 – 2007

Number of surface water bodies – 1826 Element Data – SGIData – monitoring Number of WB with existing measurements Number of WB with existing measurements (%) Number of WB with existing measurements Number of WB with existing measurements (%) Al103456,61035,6 As104857,419110,5 Cd104657,321011,5 Cr104357,11457,9 Cu104657,321211,6 Hg104757,320411,2 Ni21711,919410,6 Pb104557,221011,5 Zn104857, Input data - National database ( ) -Database of SWMA ( ) -Database of State Geological Institute – unrepeated data

Conceptual model of background levels calculation for surface water bodies

Input data samples for BL estimation in surface water: monitoring network of the Slovak winter precipitations ( )

Input data samples for BL estimation in surface water: As distribution in the rock environment

Input data samples for BL estimation in surface water: As distribution in soils – C horizon

Input data samples for BL estimation in surface water: As distribution in stream sediments

GIS system for supporting of background levels estimation

Background level of arsenic for surface water bodies in Slovakia As in ug/l Mean2.29 Median1.6 Mode1 Range59 Minimum1 Maximum60 Count1742 Statistics: General Reference Value for As in surface water (according Slovak legislation): 30 ug/l New proposal (AA-EQS): 24 ug/l

Example: Final proposal of background level of As for surface water bodies in Slovakia Legend: Arsenic (ug/l)

Schematic map with distribution of highest cumulative BL for selected metals

Uncertainty in estimating the background levels representativeness of the monitoring network in relation to the delineation of water bodies, different analytical techniques used during the monitoring period , different levels of background concentrations estimated from water bodies with data and without data, the evaluation was not considered to flow, which affects the content of the elements in surface water, allocation of contributing surfaces, contributing to water bodies.

Recommendations Analytical chemistry - application of analytical techniques and procedures for reducing LOQ and learning outcomes and processes of membrane filtration in water samples. Verification of estimated background levels in areas with occurrence of mineralized zones and ore deposits. Determination of macro-elements background levels in surface water and characterization of basic chemical types of surface water. Carefully review the relationship of background levels to determine the EQS for metals and non-priority substances

Thank you for your attention