Ecological impacts of long-term application of biosolids to a radiata pine plantation

Terrestrial bioassays for assessing the biochemical and toxicological impact of biosolids application derived from wastewater treatment plants

Wastewater treatment plants (WWTP) are facilities where municipal wastewater undergoes treatment so that its organic load and its pathogenic potential are minimized. Sewage sludge is a by-product of this process and when properly treated is preferentially called "biosolids". These treatments may include some or most of the following: thickening, dewatering, drying, digestion, composting, liming. Nowadays it is almost impossible to landfill biosolids, which however can well be used as crop fertilizers. Continuous or superfluous biosolids fertilization may negatively affect non-target organisms such as soil macro-organisms or even plants. These effects can be depicted through bioassays on terrestrial animals and plants. It has been shown that earthworms have been affected to various degrees on the following endpoints: pollutants' bioaccumulation, viability, reproduction, avoidance behavior, burrowing behavior. Collembola have been affected on viability, reproduction, avoidance behavior. Other terrestrial organisms such as nematodes and diplopods have also shown adverse health effects. Phytotoxicity have been caused by some biosolids regimes as measured through the following endpoints: seed germination, root length, shoot length, shoot biomass, root biomass, chlorophyll content, antioxidant enzyme activity. Very limited statistical correlations between pollutant concentrations and toxicity endpoints have been established such as between juvenile mortality (earthworms) and As or Ba concentration in the biosolids, between juvenile mortality (collembola) and Cd or S concentration in the biosolids, or between phytotoxicity and some extractable metals in leachates or aquatic extracts from the biosolids; more correlations between physicochemical characteristics and toxicity endpoints have been found such as between phytotoxicity and ammonium N in biosolids or their liquid extracts, or between phytotoxicity and salinity. An inverse correlation between earthworm/collembola mortality and stable organic matter has also been found. Basing the appropriateness of biosolids only on chemical analyses for pollutants is not cost-effective. To enable risk characterization and subsequent risk mitigation it is important to apply a battery of bioassays on soil macro-organisms and on plants, utilizing a combination of endpoints and established protocols. Through combined analytical quantification and toxicity testing, safe use of biosolids in agriculture can be achieved.

Impact of long-term application of biosolids to surface water nitrogen in a working forest plantation in King County, Washington

Forest fertilization with municipal biosolids has been shown to increase tree growth and enhance forest soils. However, there are concerns that nitrogen from the biosolids could impact surface waters through movement from subsurface flow. Here we analyzed data on soil and surface water nitrogen from a working tree plantation that has used biosolids for over three decades to see if there was evidence of N movement through the soil to surface waters. GIS (Geographic Information System) was used to map application units over time and LiDAR (Light Detection and Ranging) was used to delineate watersheds. The program is located in King County Washington with biosolids provided by the King County Wastewater Treatment program. We assembled records to determine if there is any evidence of movement of NO3- through soils or any enrichment in surface waters. While soils show evidence of NO3- enrichment following biosolids application with cumulative loading rates up to 26 Mg ha-1, this is generally limited to the 'A' soil horizon and does not increase linearly with increased biosolids loading rates. There was no indication of increased surface water NO3- concentration relative to biosolids application rates, with a small trend of decreasing water NO3- over time. Surface water NO3- concentration was not correlated with the fraction of the watershed area that had been amended with biosolids, and there was no observable increase in surface water NO3- with increased frequency of biosolids applications to the tree plantations. These results suggest that the current biosolids program is sufficiently protective of ground and surface waters. These observations suggest that biosolids application can be conducted on a large scale with multiple benefits and no discernible impact to surface waters.

Assessing the potential chronic, sublethal and lethal ecotoxicity of land-applying biosolids on Folsomia candida and Lumbricus terrestris

The ecotoxicity of biosolids has been studied extensively using single-compound toxicity testing and 'spiking' studies; however, little knowledge exists on the ecotoxicity of biosolids as they are land-applied in the Canadian context. The purpose of this study is to elucidate the chronic, sub-lethal (i.e., behavioural), and lethal impacts of land- applying biosolids on the environmentally relevant Folsomia candida (springtails) and Lumbricus terrestris (earthworms) and concomitantly ascertain whether the use of biosolids for nutrient amendment is a sustainable practice. This study is part of a larger multi-compartment programme which includes terrestrial plants and aquatic arthropods. After a review of existing government protocols and research, the current study suggests new environmentally relevant bioassays as to elucidate the true nature of the potential ecotoxicity of land-applying biosolids, within a laboratory context. Specifically, protocols were developed (e.g., shoebox bioassays for L. terrestris sub-lethal testing) or modified (e.g., using Evans' boxes (Evans 1947) for chronic and sub-lethal testing on L. terrestris). Subsequently, two biosolids were tested on springtails and earthworms using avoidance and reproductive bioassay endpoints, at application rates that represent standard (8 tonnes ha^-1) and worst-case scenarios (22 tonnes ha^-1). Results indicated no effect of biosolids at the environmentally relevant concentration; the worst-case scenario exhibited a positive significantly significant relationship (indicating preference for treatment conditions). We suggest that further assessment of the potential ecotoxicological impact of biosolids employ (i) environmentally relevant organisms, (ii) appropriate bioassays including the use of whole-organism endpoints, and (iii) multi-kingdom testing (e.g., Kingdom Plantae, Animalia) to comprehensively elucidate answers. Lastly, in situ (field assays) are strongly encouraged for future studies.

Carbon balance for biosolids use in commercial Douglas Fir plantations in the Pacific Northwest

Municipal biosolids are commonly used to fertilize Douglas fir (Pseudotsuga menziesii) plantations in the Pacific Northwest. An intensive soil sampling was conducted to quantify the effects of long-term biosolids application on soil carbon, nitrogen and bulk density for forest soils. This information was used to calculate a carbon balance for biosolids use in commercial tree plantations. Paired control and treated sites on two soil series (Klaus and Tokul) were included with samples collected to a 30 cm depth. A significant decrease in bulk density for two depths, but no changes in total C or N were observed in the Klaus soil. In the Tokul soil, biosolids fertilization increased C storage (total C * bulk density) for three of the four measured depths, resulting in an increase in total C from 112.8 Mg C ha^-1 to 172 Mg C ha^-1 for the 0-30 cm depth. A comparable increase in N was observed, with significant increases in N storage for all measured depths. The C balance considered fuel use associated with transport and application as costs. The fertilizer (N and P) content of the biosolids and changes in soil C were considered as credits. The balance showed net sequestration for both soil series. Carbon benefits for the Klaus soil totaled -0.2 Mg CO₂ per Mg biosolids. Benefits in the Tokul soil totaled -5.15 Mg CO₂ per Mg biosolids. Based on diameter at breast height (DBH) biosolids use also resulted in increased tree growth for both soil series. However, differences in stand age and stocking rate complicated interpretation of these results.

Long-term effects of liquid swine manure land surface application in an apple orchard field on soil bacterial community and heavy metal contents in apple (Malus pumila Mill.)

This study investigated the impact of liquid swine manure (LSM) land surface application in an apple orchard on soil health and copper (Cu) and zinc (Zn) in soil and apple. Three apple plots were selected, among which two for LSM application for 5 (AY5) and 11 (AY11) years with different application rates, a long-term inorganic fertilizer application plot as the control treatment (AY0). The soil and apple samples were collected for analysis of soil physicochemical properties, bacterial diversity and abundance, and the contents of Cu and Zn in soil and apple. Results showed that the LSM application significantly increased the concentration of soil nutrients with the highest in AY5, which has a high application rate of LSM. After 5 or 11 years applied, the content of total nitrogen (TN) in AY5 and AY11 increased by 125.2% and 96.7%, total phosphorus (TP) increased by 167.6% and 148.6%, and soil organic matter (SOM) increased by 180.7% and 120.6%, respectively. The AY5 treatment significantly lowered OTUs and decreased Shannon index trend with a negative correlation between soil organic matter and Shannon index. The six predominant bacterial phyla in different treatments were similar, but the LSM application significantly increased the abundance of Chloroflexi and Firmicutes. However, the abundance of Actinobacteria and Acidobacteria significantly decreased in AY5 as compared to control treatment, followed by a significant positive correlation between the abundance of Acidobacteria and soil pH. Besides, LSM application significantly increased the contents of soil Cu, Zn, and apple Zn. Overall, the results illustrated that appropriate application rate of LSM can effectively improve apple orchard soil quality and bacterial community structure, but it will increase the risk of heavy metal accumulation in soil and apples.

Effect of biosolids on the nitrogen and phosphorus contents of soil used for sugarcane cultivation

The application of biosolids improves soil nutrient availability and crop productivity; however, their application needs to be carefully evaluated so as to avoid the risk of contamination. In this study, a 12-month field experiment using a randomized block design with factorial arrangement was conducted to evaluate the effects of biosolids on the nitrogen and phosphorus contents of a sugarcane-cultivated inceptisol. Three types of dewatered biosolids were used: anaerobically digested (B), anaerobically digested and thermally dried (BST), and anaerobically digested and lime-stabilized (BA) biosolids. The results showed that biosolid use increases soil nitrogen content by up to 37% of the total Kjeldahl nitrogen, 42% of NO₃⁻, 13% of NO₂⁻, and 32% of NH₄⁺. Biosolid treatments exceeded the phosphorus requirement for sugarcane cultivation by up to 277% for B, 170% for BST, and 368% for BA. The application of biosolids sufficient to meet crop nitrogen requirements significantly increased soil phosphorus content, suggesting an overdose and low crop response to the available phosphorus. The application of biosolids yielded results similar to those of mineral fertilizers, suggesting their potential use in agriculture.

Amendment of municipal sewage sludge with lime and mussel shell: Effects on fate of organic matter and pharmaceutically active compounds

The deterioration in its strength from long-term degradation of organic matter and release of pharmaceutically active compounds (PhACs) have caused adverse environmental effects in municipal sewage sludge (MSS) landfill. Lime and a mixture of lime and mussel shell were employed as potential stabilization agents for MSS in this work. Their efficacy was assessed by investigating the effects on transformation of organic matter, as well as the occurrence and fate of four PhACs (fluoxetine, gemfibrozil, triclosan and carbamazepine) over 42 days. The addition of the selected agents: (i) prevented the microbial degradation of organic matter; (ii) modified the predominant functional groups of amide groups (amide I and II) and polysaccharides to deprotonated carboxylic groups and destruction of amide groups; and (iii) shifted the abundance of organic constituents from microbial by-products to humic acid-like organics with conformational changes. The measurement method provided reliable and precise results for determining PhAC concentrations in MSS with and without amendment, although matrix effects and process effects were found to affect measurement sensitivity. Available fractions of the PhACs increased in MSS with lime addition, but decreased in the presence of the mixture of lime and mussel shell due to the strong adsorption effects of the shells. The mixture of lime and mussel shell would be recommended for stabilizing MSS prior to being landfilled. However, longer term and larger scale investigation may be needed to better evaluate the applicability of lime and mussel shell for reducing the hazards and facilitating the management of MSS.

Comparative analysis biochar and compost-induced degradation of di-(2-ethylhexyl) phthalate in soils

In recent years, biochar has been extensively studied as a sorbent for immobilizing contaminants and minimizing their bioavailability in soils. Few studies have been conducted to evaluate the interactions between biochar and compost in soils and their impact on degradation of organic contaminants. In the present study, soils with high organic carbon content (HOC) and low organic carbon content (LOC) were spiked with 100mg·kg^-1 di-(2-ethylhexyl) phthalate (DEHP) amended with biochar derived from dead pigs, bamboo, and composted sheep manure. The soils were thereafter incubated for 112days at 25°C and periodically sampled for monitoring DEHP concentrations. Degradation of DEHP was described by a logistic model. Results showed that the initial degradation rates were slow, but accelerated after 14days of incubation. The DEHP degradation rates were higher in the HOC soils than in the LOC soils over the incubation period. The half-lives of DEHP were shorter in the LOC soils treated with pig biochar, and bamboo/pig biochar plus compost than in the untreated soil. However, there was no significant difference in the half-lives of DEHP in the HOC control and treated soils. The differential effects of soil amendments on DEHP degradation between LOC and HOC soils could be explained by the properties of the organic amendments, soil pH and the organic carbon contents of the soils.

Potential Use of Biosolids to Reforest Degraded Areas with New Zealand Native Vegetation

Biosolids could potentially be used for reforestation of degraded soils in New Zealand with native vegetation. Many native plant species of New Zealand thrive in low-fertility soils, and there is scant knowledge about their nutrient requirements. Therefore, it is unclear whether they will respond positively to the addition of biosolids. We used a pot trial to determine the responses of 11 native plant species to biosolids addition (10% w/w, ∼90 Mg hm) on two distinct degraded soils, Lismore stony silt loam and a Kaikōura sand. We also intended to prove that the soil microbial activity improves with the addition of biosolids, depending on the plant species. All species grew better in Lismore stony silt loam than the Kaikōura sand. All species in the Lismore stony silt loam responded positively to biosolids. The response to biosolids addition in the Kaikōura sand was variable, with four species showing no improvement in growth when biosolids were added. The nutrient status (N, P, S, Cu, and Zn) of all species improved when the two soils were amended with biosolids. However, some plant species, especially Sol. ex Gaertn. and Raoul, showed concerning concentrations of Cd (up to 2.4 mg kg). Dehydrogenase activity of soils (indicator of soil microbial activity) increased in biosolids-amended soils, with a strong species effect. Future work should involve field trials to determine the effect of biosolids addition on the establishment of native plant communities.

Persistence of Ascaris spp. Ova in Tropical Soil Cultivated with Eucalyptus and Fertilized with Municipal Biosolids

In many countries, the main reason for severely restricting or outright banning the land application of class B biosolids is the lack of risk assessment for adverse human health impacts. Among pathogens that are not often studied are helminth ova, including that of the spp. Almost all of the knowledge about the persistence of spp. ova in soils fertilized with biosolids is based on studies developed in North America, Europe, and Asia. These studies have almost always been conducted under temperate climate conditions, which may cause erroneous interpretations when the conclusions are extrapolated to tropical regions such as those found in Brazil. This team evaluated the persistence of viable spp. ova in a sandy Quartzipsamment tropical soil, previously planted with × hybrid () and fertilized with biosolids, over a 52-wk period. During the reporting period, the average temperature of soil and biosolids fluctuated between 15 and 30°C, and the average moisture of biosolids fluctuated between 60 and 90%. The estimated persistence time of viable spp. ova after land application was estimated at close to 7 wk, indicating that ova may not be viable for as long as it has been shown to be in studies of more temperate areas. The relationship of temperature with persistence of viable spp. ova in a tropical soil was stronger than moisture content, suggesting that temperature substantially contributed to their nonviability over the course of the experiment.