Specialist Group on Use of Macrophytes in Water Pollution ... - IWA

flow regime, hydraulic retention time), soil matrix, vegetation type and density, and
environmental conditions such as temperature, oxygen regime, and solar irradiation.
Estrogens are relatively hydrophobic compounds (log Kow 2.81-4.67), thus one of the
mechanisms by which they can be removed is sorption to hydrophobic surfaces (e.g., organic
rich soils; White et al., 2006; Matamoros and Bayona, 2008). Similar to other organic
compounds, estrogens are also exploited and degraded by microorganisms (e.g., Matamoros
and Bayona, 2008; Imfeld et al., 2009). Another possible mechanism for estrogen breakdown
is photo-degradation; however this is relevant only to surface flow wetlands, particularly
shallow and clear ones (White et al., 2006). The low vapor pressure of estrogens makes
evaporation a less probable mechanism for removing them in wetlands (Ingerslev and
Halling-Sørensen, 2003).
Evidence for estrogen removal in wetland systems
Elimination of estrogenic compounds from wastewater is expressed either by decrease in
concentration or by decline in estrogenic activity (estrogenicity). Here we present the data for
different types of constructed wetlands, in order of increasing rate of attenuation.
Surface flow wetlands (SF)
Data on removal efficiency of estrogens or estrogenicity in surface-flow wetlands are
conflicting. Some reports contend that there is no or little attenuation of estrogens, while
others report measurable removal. Insignificant removal of estrogenic activity was
demonstrated for example in the Prado wetland (Riverside, California; Xie et al., 2004)
treating the water of the Santa Ana River that receives tertiary-treated effluent (Bachand and
Horne, 2000). The river water was discharged into 50 shallow SF ponds (average depth 0.75
to 0.92m) with average discharge of 3.6m 3 /s, and hydraulic retention time (HRT) of 6 days.
No difference in esterogenicity (in vivo rainbow trout vitellogenin expression and in vitro
yeast estrogen screening assays) was found between river water entering and leaving the
Prado wetland. Persistence of estrogenic compounds (E2, E1; maximum concentration of 4
and 12 ng/l, respectively) was also found in shallow interconnected engineered ponds
receiving municipal secondary effluent with an HRT of 6-7 days (Kolodziej et al., 2003). In a
study in Illinois, Peterson and Lanning (2009) reported the failure of an SF system (3
consecutive cells, 6X15X1.2m, each with a variety of emergent and floating macrophytes),
receiving secondary municipal effluent (ca. 11.4 m 3 /day; 4 days mean HRT), to significantly
remove E2 and E1 (mean influent concentration 32.8-55.5 and 73.6-74.8 ng/l, respectively).
The authors found only poor removal of E2 (13%) and failure to remove E1 in a similar
surface flow system that had only floating aquatic plants (duckweed and algae). Difference in
the removal of E2 by the above SF systems was attributed to different plant composition. We
examined removal of E2 and E1 in an hybrid wetland in Israel where an SF pond (25m 2 ,
depth – 0.55m, a variety of emergent and submerged macrophytes; discharge 12m 3 /day;
calculated HRT – ca 15 hrs) provided final treatment (Milstein et al., in preparation). We too
found no significant removal of E2 (influent concentration of E2 2.7ng/l; E1 was below
detection limit of