Effect of DOM quality and quantity on transport and degradation of pesticides Karlien Cheyns, Mariangiola Mollicone, Stien Van Gestel Dirk Springael, Erik Smolders, Jan Diels 01/02/2007

Objectives Physico-chemical? - DOM-related transport and competition ? ? Biodegradation? - availabilty? - DOM as C-source (catabolic repression, extra C-source, effect on microbial diversity) DOM influences pesticide transport in soil To predict the effects of DOM on transport and degradation of pesticides with emphasis on the subsoil environment To unravel how DOM quality and quantity affect the dynamics/activity and competence of pesticide degrading populations with emphasis to the subsoil environment

Hypotheses H1: Effects of DOM on transport of pesticides (Trifluralin) depends on the structure of DOM and can be predicted from batch sorption test H2: Effects of DOM on pesticides (Atrazine) degradation in (sub)soil is the net result of effects on bioavailability and on population dynamics H3: The final effect of DOM on the fate of pesticides in soil depends on DOM structure and is concentration dependent Task 1: Study of the physico- chemical interactions between DOM, soil and pesticides Task 2: Study of the effect of DOM on pesticide degradation Task 3: Study of the net-effect of DOM on pesticide transport and biodegradation in soil columns Task 4: Effect of DOM on the transport of pesticides in field experiments

Task 1: Study of the physico- chemical interactions between DOM, soil and pesticides Task 2: Study of the effect of DOM on pesticide degradation Task 3: Study of the net-effect of DOM on pesticide transport and biodegradation in soil columns Task 4: Effect of DOM on the transport of pesticides in field experiments

Physico-chemical interactions Emphasis on 2 pesticides (herbicides) –Atrazine: Log K ow = 2,7  Expected low K DOC –Trifluralin: Log K ow = 4,83  High K DOC

Effect of DOM on atrazine sorption Batch sorption tests with or without extra DOC: –Solution of AT (~100 µg/L) and different DOM shaken with soil (2:1 l:s) –After equilibrium (24h): analysis of AT and DOC concentration in supernatans

Effect of DOM on atrazine sorption

Effect of DOM on trifluralin desorption Trifluralin: low solubility in water  first spiking soil, then desorption tests in batch with different DOM solutions Fresh soil TM (2mm) Treflan (19,2 mg TFL/kg) 14 C Trifluralin (150 µg/kg)

Effect of DOM on trifluralin desorption Batch experiments 2 g spiked soil 10 ml DOM solution 24 h desorption 2 g control soil 10 ml DOM solution Quench control 5 ml -> counter 3 ml -> TOC analyser 5 ml + known # 14 C TFL -> counter

Effect of DOM on trifluralin desorption Theory desorption with DOC –K d * = K om oc/(1+K DOC C DOC ) –Estimate K om from logK om =0,72logK ow + 0,49 (Schwarzenbach and Westall, 1981) logK ow =4,83 => logK om = 3,97

Effect of DOM on trifluralin desorption Theory desorption with DOC

Effect of DOM on trifluralin desorption Influence pig manure (< 0,45 µm) on TFL desorption

Effect of DOM on trifluralin desorption Influence Aldrich Humic Acid on TFL desorption (low DOC concentrations)

Effect of DOM on trifluralin de- and adsorption Testing reversible sorption: –Use supernatans from desorption test with TFL spiked soil –Add non-spiked soil with low C content –Equilibrate on shaker –Measure 14 C-TFL and DOC concentration of supernatans

4 g spiked soil 20 ml CaCl M Desorption 5 ml -> counter 3 ml -> TOC analyser Effect of DOM on trifluralin de- and adsorption 0,5 g clean soil, (0,18 % C) 10 ml solution + 14 C TFL Adsorption 5 ml -> counter 3 ml -> TOC analyser

Effect of DOM on trifluralin de- and adsorption Testing reversible sorption: -> If reversible sorption: expect 1,4 µg/l after adsorption

Conclusions task 1 (physico-chemical interactions) Atrazine: –No expected DOM-facilitated mobilisation Trifluralin: –Indications of low mobilisation from batch experiments with high DOC concentrations -> representative in field conditions? = > Future task 1 Additional de/adsorption tests of Trifluralin with DOM of different quality and quantity Test ‘enhancement solubility’ of Trifluralin in H 2 O with DOM in batch Abiotic column experiments to test if the batch sorption data explain DOM facilitated leaching

Task 1: Study of the physico- chemical interactions between DOM, soil and pesticides Task 2: Study of the effect of DOM on pesticide degradation Task 3: Study of the net-effect of DOM on pesticide transport and biodegradation in soil columns Task 4: Effect of DOM on the transport of pesticides in field experiments

Effect of DOM on pesticide degradation Two approaches –Effect of DOM on activity of pure atrazine-degrading cultures –Effect of DOM on activity of soil microbial communities

Effect of DOM on degradation of atrazine by pure cultures Atrazine-degrading cultures: –Nocardioides (SP 12), –Arthrobacter crystallopoietes (SR 30) –Chelatobacter heintzii (SR 38) (Mandelbaum et al., 1995; Radosevich et al., 1995). Atrazine concentration measured by HPLC analysis (start conc 33 mg/l)

Effect of DOM on degradation of atrazine by pure cultures Test addition of C (mixture glucose, citrate and gluconate) and DOM (CaCl M extract from Termunck soil) –Chelatobacter heintzii (SR38) MediaDOC (mg/L) MMN + C110.0 MMN + C MMN + C DOM (CaCl 2 extract) 3.6

Effect of DOM on degradation of atrazine by pure cultures Test addition of C (mixture glucose, citrate and gluconate) and DOM (CaCl M extract from Termunck soil) –Arthrobacter crystallopoietes (SR30) MediaDOC (mg/L) MMN + C110.0 MMN + C MMN + C DOM (CaCl 2 extract) 3.6

Effect of DOM on degradation of atrazine by pure cultures Effect of DOM on the maximal degradation rate –Chelatobacter heintzii (SR38) –Arthrobacter crystallopoietes (SR30)

Effect of DOM on mineralisation of atrazine by soil communities Mineralisation experiments: –0,2 g soil + 5 ml medium –~ 50 µg/l 14 C atrazine –NaOH trap (1 ml 0,5 M) to catch 14 C-CO 2

Effect of DOM on mineralisation of atrazine by soil communities Sample Last treatment Treatment time [years] Max mineralization rate [%/day] Lag time [days] Mineralistation extent [% initial 14 C] Bev Bev Lub TW En En Ep

Effect of DOM on mineralisation of atrazine by soil communities Setup: –0,2 g soil + 5 ml medium –Different media: Mineral medium without N (MMN) CaCl M DOM extracted from 3 ≠ soils (TM, 18, 73) with CaCl M –Atrazine 14 C: initial: ~ 38 µg/l –Topsoil samples

Effect of DOM on mineralisation of atrazine by soil communities DOM from soil 73 (different concentrations) in CaCl M

Effect of DOM on mineralisation of atrazine by soil communities DOC concentration in time

Effect of DOM on mineralisation of atrazine by soil communities Mineralisation capacity tested in different depths –Sampling in depth (0-60 cm) –Different depths, seperatly incubated: 0-15; 17-30; 32-45; cm

Effect of DOM on mineralisation of atrazine by soil communities CaCl 2 extract -> TOC measurement; divided by kg dry soil No clear effect in depth

Effect of DOM on mineralisation of atrazine by soil communities 3 samples, 4 depths

Effect of DOM on mineralisation of atrazine by soil communities Different depths + different media: –DOM: extracted from TM soil (DOM TM) –DOM: Aldrich Humic Acid (AH) –DOM: Humic Acid extracted from Zegveld soil (ZH) –Salt solution which imitates TM extract without organic matter –CaCl M as control

Conclusions Task 2 (pesticide degradation) Indications that degradation of atrazine by pure atrazine-degrading cultures was enhanced by additional C Mineralisation rate of atrazine in soil was in few cases inhibited by certain DOM solutions -> quality important? In depth: faster and higher mineralisation in topsoil, other layers no clear effect of depth DOC influence on mineralisation in depth: inhibition by DOM extracted from TM at each depth, but unclear effects of other C-sources = > Future task 2 Examine effect of other DOM with different quality and quantity on atrazine degradation Examine effect of DOM on soil microbial activity (glucose respiration, nitrification potential) Analyse effect of DOM on dynamics of soil communities by means of 16S rDNA based DGGE Analyse effect of DOM on dynamics and activity of atrazine degraders by qPCR

Task 1: Study of the physico- chemical interactions between DOM, soil and pesticides Task 2: Study of the effect of DOM on pesticide degradation Task 3: Study of the net-effect of DOM on pesticide transport and biodegradation in soil columns Task 4: Effect of DOM on the transport of pesticides in field experiments

Field experiment Trifluralin added on all plots Measurement of trifluralin in samples? –Kd~75 -> retention time high?

Thanks for your attention ! Questions?