Phenol, 4-nonyl-, branched

Biodegradation in soil

Description of key information

Trocmé et al. (1988) studied the fate of nonylphenol (NP; 100 mg/kg and 1,000 mg/kg) in a simplified soil system and its effect on microbial activity. The artificial soil system consisted of sewage sludge compost (1/3 dry matter) and sandstone (2/3 dry matter). The cells were incubated at 60% field moisture capacity at 25°C in the dark for 40 days.

150 d microcosm experiments were conducted (Dettenmaier et al., 2007) to evaluate the mineralization and plant uptake of [14C]nonylphenol (NP) in a soil/biosolids (99.5:0.5 w/w) environment planted with crested wheatgrass at 3 initial nominal concentrations (6, 24, and 47 mg/kg dry wt). The biosolids were obtained from a municipal treatment plant, and the loamy sand soil was freshly collected. Incubation was conducted at a day/night temperature of 20/16 +/- 1°C and a 16:8-h light:dark photoperiod.

Topp et al., 2000, also studied the biodegradation of 4-nonylphenol in laboratory microcosm experiments with agricultural, noncultivated temperate and Arctic soil with an incubation duration of 40 days at temperatures between 4 to 30 °C and different moisture content (water holding capacity, air-dried, and two intermediate values).

In a 110 d lysimeter study conducted by Jacobsen et al. (2004), NP was added to loamy sand soil with sewage sludge to obtain initial concentration of 0.56 mg NP/kg dry weight. The lysimeters were grown with barley to mimic field conditions..

Mortensen et al. (2003) studied the degradation and possible uptake of NP in agricultural plants in greenhouse pot experiments grown with rape. Different waste products including anaerobic and aerobic sludge, compost, and pig manure were incorporated in sandy soil. In addition, NP was used to spike soil to known concentrations. The concentrations in the soil were between 13 and 534 ppb dry weight.

Additional information

Trocmé et al. (1988) monitored the effect of nonylphenol (100 and 1000 ppm) on CO₂ evolution and biomass adenosin triphosphate (ATP). Nonylphenol depressed CO₂ production significantly only at high concentrations (1000 ppm 4-nonylphenol). Biomass ATP declined progressively after the 5th day. At 100 ppm no toxic effects were detected. After a 5 day lag phase, nonylphenol disappeared readily upon incubation at the lower concentration (100ppm, 89% degradation after 40 days), but persisted at high levels (1000ppm, 62% degradation after 40 days). NP loss was rapid at first then slowed down. The persistence of 4-nonylphenol increased under aseptic conditions (76% nonylphenol recoverable after 24 days). In both samples volatilisation was insignificant with 0.22% volatilisation over 40 days in the 1,000 mg/kg sample. The lack of transformation under the 1000-ppm treatment or under semi-sterile conditions seems to indicate that different processes, such as residue binding, may take place. The authors suggested that nonylphenol underwent microbial degradation after a period of induction of the microorganisms.

In the experiment conducted by Dettenmaier et al. (2007) mineralization (to CO2) was 7% for NP and was independent of the initial exposure concentration of 6 to 47 mg/kg. The presence of crested wheatgrass did not enhance the percentage mineralization. Degradation of NP in soil based on test material analyses was 90% at the end of the study. Calculated half-lives for NP averaged from 31 to 51 d in the various planted, unplanted, and unplanted aseptic systems.

Topp et al. (2000) could demonstrate that at 30 °C, [U-ring-14C]4 -nonylphenol was rapidly mineralized without a lag in the six soils tested. The 4 -nonylphenol mineralization did not occur in autoclaved soil. The response of 4-nonylphenol mineralization to variation in temperature and moisture content was consistent with an aerobic biological mechanism of degradation. Mineralization of [U-ring-14C]4 -nonylphenol was rapid in the concentration range of 1 to 250 mg/kg soil dw. Sludge solids did not inhibit 4-nonylphenol mineralization, although sewage sludge at high concentrations was inhibitory, apparently because of high BOD. GC-MS analyses of extracts prepared from soil incubated with commercial nonylphenol indicate that all detectable isomers were degraded. Half-lives estimated from the initial (rapid) mineralization rates of 4-nonylphenol ranged between 4.5 and 16.3 d. In summary, these results indicate that microorganisms that can metabolize 4-nonylphenol are found in a wide variety of soils, including two originating from the Canadian Far North, which presumably have not been exposed anthropogenically to this chemical. It can be concluded that 4-nonylphenol should be generally biodegradable in well-aerated arable soils.

In accordance with Topp et al. (2000) Jacobsen et al. (2004) observed an initial rapid degradation in the top layer of the soil, followed by a slower but continuous degradation. After ten days 55% of NP were degraded. At the end of the experiment, the concentration of NP was below the analytical detection limit. Assuming first-order degradation kinetics, a half-life of 37 days for NP was estimated.

When NP was added to soil with waste application (Mortensen et al., 2004) and homogenous mixtures were established, plant growth stimulated the degradation process of NP. In experiments with anaerobic and aerobic sludge, respectively, 13 and 8.3 % of NP remained in the soil from pots planted with rape compared with 26 and 18 % in soil without plant growth.

When NP was added as spike to soil, the degradation was more complete and plant growth did not influence the degradation. Percentages of 2.2 and 1.8 were still in the soil after 30 days for planted and plant-free pots, respectively.

The degradation of NP in soil was affected by waste type and application form. More complete degradation of NP was observed in soil amended with sludge compared with compost-treated soil.

Results of the studies are summarizes in Table 1.

Table 1: Summary of study results

Compound (CAS Number; Purity [%])	NP Concentration tested	Test Method	Result	Medium	Experimental Conditions	Reference
4- NP Technical grade (85% pure)	100 mg/kg 1000 mg/kg	Similar to OECD 307 (Aerobic and Anaerobic Transformation in Soil); CO2 evolution	100 mg/kg: 5 day lag phase, subsequently rapid degradation; 89% degradation after 40 d   1000 mg/kg: Significant depression of CO2evolution (toxicity); 62 % degradation after 40 d   Insignificant loss of NP through volatilization	sewage sludge compost (1/3 dry matter) and sandstone (2/3 dry matter)	Temperature: 25 °C (dark) Duration: 40 d Moisture: 60% field capacity	Trocmé et al. (1988)
Ring-labeled [^14C]nonylphenol (95.7% pure)   Nonylphenol (99.7% pure)	6 – 47 mg/kg	Similar to OECD 307 (Aerobic and Anaerobic Transformation in Soil); Microcosm experiments	Mineralization (^14CO2): 7% NP, independent of initial concentration   Degradation based on soil extracts after 150d: 90%; Half-lives: 31 to 51 d in planted, unplanted, and unplanted poisoned control    No significant influence of plants on mineralization	Soil/biosolids ( 99.5 : 0.5 w/w); microcosms planted with crested wheatgrass	Temperature: 20/16 °C (day/night) Photoperiod: 16:8 light:dark Duration: 150 d Moisture: 60-80% field capacity	Dettenmaier et al. (2007)
Ring-labeled [^14C]nonylphenol (99% pure)   4-NP Technical grade	1 – 250 mg/kg	Similar to OECD 307 (Aerobic and Anaerobic Transformation in Soil); Laboratory microcosm experiments	rapid mineralization, no lag phase;   half-lives: 4.5-16.3 d   increasing mineralization with increasing temperature and optimal water content	Non-cultivated temperate and arctic soils	Temperature: 4-30 °C Duration: 40 d Moisture: air, dried, field capacity, two intermediate values	Topp et al. (2000)
Nonylphenol (purity not reported)	0.56 mg/kg	Lysimeter experiments	Half-life: 37 d	Loamy sand soil grown with barley to mimic field conditions NP added with sewage sludge	Temperature: no data Duration: 110 d Moisture: 16%	Jacobsen et al. (2004)
NP in spike solutions: synthesized, unbranched 4-n-nonylphenol NP in waste products: branched nonylphenol	NP in spiked soil: 320-534 ppb       NP in soil amended with waste products: 0-246 ppb	Greenhouse pot experiments	64 - 99.1% degradation within 30 d	Sandy soil amended with anaerobic and aerobic sludge, compost, pig manure; NP spiked soil   Pots were planted with Rape	Temperature: no data Duration: 30 d Moisture: 60% of water holding capacity	Mortensen et al. (2003)

The data available indicate that nonylphenol undergoes biodegradation in soil systems. The mineralization of NP is not dependent of the initial concentration except for very high concentrations (e.g. 1000 mg/kg, Trocmé et al., 1988) whereby it likely inhibits biodegradation of NP because of toxicity to micro-organisms.

Moreover, NP degradation in soils is dependent on soil temperature and soil moisture conditions (Topp et al., 2000) as well as on oxygen conditions. NP degradation was limited due to lack of oxygen because of high BOD of high concentrations of sewage sludge.

A factor that is important for NP biodegradation is that the nonylphenol supplied is a mixture of compounds with differing degrees of branching/isomers in the nonyl chain. It is known that in general increased branching in alkyl chains reduces biodegradability and so it may be expected that linear NP isomers degrade faster than branched NP isomers. In the degradation results of Trocmé et al. (1988) some direct evidence for this was found in the chromatographic analysis of nonylphenol at various times during the test (some nonylphenol peaks decreased faster than others). According to the UK Risk Assessment Report (2005) on 4-nonylphenol (branched) and nonylphenol, p. 60, “such an effect may explain why in many of the tests the degradation of nonylphenol appears to follow two or more “phases”, with an initial relatively rapid removal of nonylphenol followed by one or more slower phases of removal, although there are many other possible explanations for such behaviour (e.g. a reduction of viability of micro-organisms with time)”. 

Tests with ring-labeled [¹⁴C]nonylphenol demonstrate that not only the alkyl chain is subject to degradation but also the aromatic ring.

The overall conclusion from the data is that nonylphenol is biodegradable in soils and would be rapidly dissipated in well-aerated soils following application of sewage sludge. Reported half-lives for NP degradation in soil were between 4.5 and 51 d.