Research note: High levels of lead and arsenic in imported dried black soldier fly larvae: implications for backyard poultry supplementation

Abstract

Insects provide essential nutrition to poultry, however, the feedstock fed to the insects and the age and method of processing, can significantly impact nutrient and safety levels. The purpose of this research was to examine the nutrient and safety of black solider fly larvae (BSFL). Over a two-year period, 21 BSFL were purchased from retail and online establishments and blindly labeled and sent to accredited laboratories for proximate analysis, heavy metal analysis and antibiotic residues. No samples contained detectable levels of antibiotic residues. On average, Chinese-sourced dried black solider fly larvae (DBSFL), had 25X more lead and 8X more arsenic than North American, both values were statistically different. Chinese-sourced DBSFL had significantly lower phosphorus, protein, magnesium, potassium and manganese as compared to those from North America (p<0.05). While North American DBSFL had significantly lower fat and iron levels than Chinese-sourced DBSFL. Many of the imported products did not have or were not compliant with current US regulatory labeling requirements. The mislabeling and higher levels of heavy metals in DBSFL is concerning as it not only can affect the health of back yard flocks and humans via consumption of eggs from backyard flocks but also has the potential to contaminate the environment. Keywords: Dried black solider fly larva; Heavy Metal; Layer; Backyard chicken

Introduction

Import reports demonstrate that substantial volumes of dried insects, primarily mealworms and black soldier fly larvae (BSFL), are imported into the US annually. Between April 2019 and August 2024, 17,178 metric tons of dried black soldier fly larvae (DBSFL) were imported into the US, and an additional 9,663 metric tons of shipments containing a combination of DBSFL and dried mealworms, crickets, cockroaches, and/or other arthropods were imported into the USA (ImportKey, 2024). Some of these imports are used in wild bird seeds and treats, but many dried insects are marketed to backyard flock owners.

It is estimated that there are over 85 million backyard chickens in the USA, based on 9% of the US population owning an average of five chickens per household (APPA, 2023). For many, the rationale for having chickens is to provide eggs that flock owners consider to be more nutritious and safer than commercial eggs (Elkhoraibi et al., 2014). Backyard chickens are also often considered pets (APPA, 2023). The majority of of backyard chickens are laying hens (61%), followed by meat birds (32%), game birds, and show birds, with almost 25% ownership in the latter two categories (APPA, 2023).

When feeding backyard poultry, flock owners may allow hens to forage for naturally occurring food items in their environment. They may also provide complete poultry diets or scratch grains, and/or may provide supplements intending to augment nutrition along with complete feeds or natural foraging. Based on 2022 surveys, 58% of backyard flock owners purchase feed for their chickens, 32% purchase treats, and 28% purchase supplements (APPA, 2023). Insects are a natural part of free-ranging poultry diet, and many backyard flock owners choose to provide dried insects as a supplemental food item or as a treat. The rate at which insects are fed may vary substantially by owner and season.

Insects provide essential nutrition to poultry, in the form of amino acids, fatty acids, vitamins, and minerals. However, the diet upon which that insect is reared, and the age and method of processing, can significantly impact nutrient levels (Oonincx et al., 2015). DBSFL can bioaccumulate minerals and thus the mineral content of their feedstock can directly impact the mineral content of the DBSFL (Finke et al., 2013). Furthermore, the diet a laying hen consumes not only affect her health but can also transfer to the egg and effect human health. Given the large numbers of backyard flocks in the US; the rapid rise in the use of dried insects as a food item for these birds; and the potential variation in nutrient and mineral content of insects. The purpose of this research was to examine the nutrient and safety levels of DBSFL available from retail and online establishments, source domestically and internationally.

Materials and methods

Twenty-one (21) samples of DBSFL were sourced at retail stores and online over two years (2023-2024). The DBSFL purchased were selected based on their country of origin and products that had a high market share. Based on product packaging and label claims, the origin of the DBSFL were identified and grouped into thirteen (13) products sourced from China, four (4) from North America, and five (5) that had no identified country of origin. No single retail brand/product was duplicated in these analyses. Retail packages were opened and subsampled and sent to respective labs with brand names and country of origin concealed.

In 2023, product samples were analyzed for proximate analysis (moisture via AOAC 930.15; protein by combustion via AOAC 990.03 and 992.15 with 6.25 protein correction factor; crude fat by acid hydrolysis via AOAC 954.02; crude fiber via AOAC 962.09 and AOCS Ba6-84; ash via AOAC 942.05; nutritional minerals via modified AOAC 984.27, 985.01, and 2011.14); antibiotic residues (ampicillin, bacitracin, carbadox, chlortetracycline, clarithromycin, erythromycin, furazolidone, olaquindox, oxytetracycline, penicillin G, salinomycin, spiramycin, sulfadiazine, sulfamethazine, tylosin, and virginamycin M1] via internal method); and heavy metals (aluminum, barium, beryllium, boron, strontium, and vanadium via modified AOAC 984.27, 985.01, and 2011.1, arsenic, cadmium, lead, and mercury via AOAC 2011.19, 993.14 and 2015.01), where the limit of detection for heavy metals is between 2.5-10 ppb (details available in AOAC). All analyses in 2023 were conducted by Eurofins, www.eurofins.com, at ISO 13044 certified laboratories.

In 2024, product samples were analyzed for heavy metals as per 2023 (Eurofins, www.eurofins.com) and for proximate analysis (moisture via AOAC 930.15; crude protein via AOAC 990.03 with 6.25 protein correction factor; crude fat by acid hydrolysis via AOAC 954.02; crude fiber via AOAC 978.10; ash via AOAC 942.05; and nutritional minerals via AOAC 985.01). All proximate analysis in 2024 were conducted by Cumberland Valley Labs, www.foragelab.com.

Data were compiled, and mean (arithmetic), range, and standard error of the mean calculated, and compared to packaging guarantees. Statistical analysis was conducted using a paired t-test (JMP, SAS Institute, Cary, NC), with significance at p<0.05, only to compare DBSFL between origin that was clearly identified on packaging (e.g., unknown source DBSFL were not compared other than for mean, range, and standard error of the mean). Statistical analysis was not conducted on nutrients when there were no or few samples that were higher than the limits of detection.

Results and discussion

The results of selected nutrient analyses are presented in Table 1. No samples contained detectable levels of antibiotic residues (data not shown). Proximate analysis and nutritional minerals varied between Chinese and N. American DBSFL. Crude protein content was significantly lower, and crude fat was significantly higher for Chinese sourced DBSFL compared to those from N. America (p<0.001. Overall, crude fiber, calcium, ash, sodium, copper, and zinc levels were similar between DBSFL sources. Phosphorus was significantly lower in Chinese-sourced DBSFL as compared to those from N. America (p<0.05). Magnesium, manganese, and zinc were significantly lower in Chinese-sourced DBSFL as compared to those in N. America (p<0.05 for each). Iron was significantly higher in Chinese-sourced DBSFL, and double that of N. American DBSFL (p<0.02). This variation in nutrient content may be due to life stage at harvest or dietary feedstock (Oonincx et al., 2015).

Table 1.

Nutrient and heavy metal content of dried black soldier fly larvae (DBSFL) from retail products from 2023-2024. Chinese-sourced DBSFL (n=13), N. American sourced DBSFL (n=4), and samples of unidentified origin (n=5) were analyzed for proximate composition, nutritional minerals, and heavy metals.

	Overall mean	SEM	Range (min-max)	Mean of DBSFL of Chinese origin	SEM	Mean of DBSFL of N. American origin	SEM	p value
Moisture (%)	5.1	0.15	4.1-6.3	5.0	0.15	5.6	0.35	0.105
Crude Protein (%)	38.5	0.84	32.3-45.4	36.7	0.47	43.3	0.97	<0.001
Crude Fat (%)	37.2	1.14	25.5-43.0	39.6	0.82	32.1	1.00	<0.001
Crude Fiber (%)	8.3	1.07	5.0-18.2	5.5	0.20	8.0	1.18	0.259
Ash (%)	11.2	0.91	6.3-22.6	11.4	0.66	10.7	3.96	0.762
Calcium (%)	3.33	0.28	1.58-5.57	3.62	0.316	2.26	0.57	0.054
Phosphorus (%)	0.71	0.033	0.54-1.15	0.66	0.025	0.78	0.040	0.035
Magnesium (%)	0.24	0.019	0.07-0.47	0.22	0.008	0.29	0.029	0.004
Potassium (%)	0.94	0.052	0.13-1.19	0.95	0.028	1.08	0.078	0.050
Sodium (%)	0.18	0.019	0.03-0.39	0.19	0.021	0.13	0.011	0.135
Copper (ppm)	20.4	3.63	8.0-52.0	23.6	4.90	15.5	1.04	0.386
Manganese (ppm)	63.1	11.67	10.2-173.0	40.4	3.29	118.6	37.73	0.002
Zinc (ppm)	107.8	32.18	36.5-672.0	81.0	9.04	98.0	7.38	0.337
Iron (ppm)	363	34.9	57.7-667.0	400	39.1	200	47.7	0.019
Arsenic (ppb)	414	129.3	30-2,620	511	179.9	62.0	26.2	0.195
Cadmium (ppb)	232	41.6	40-734	260	59.3	196	54.3	0.576
Lead (ppb)	648	250.7	23-4,930	784	353.1	31.0	2.8	0.266
Strontium (ppm)	71.7	9.95	7.0-114.0	87.6	3.5	7.0	0.0
Aluminum (ppm)	133.8	21.65	7.8-260.0	199.0	23.9	7.8	0.0
Barium (ppm)	13.3	2.60	3.0-30.4	12.4	1.6	3.0	0.0
Boron (ppm)	3.6		<2.48-3.6	<2.48	0.0	3.6	0.0
Antimony (ppb)	23.6	2.02	17.9-36.0	28.0	3.0	<2.5	0.0
Chromium (ppb)	2.5	0.01	<2.5-2.54	3.0	0.0	<2.5	0.0
Mercury (ppb)	15.9		<5.0-15.9	<5.0	0.0	<5.0	0.0

Beyond nutrient level, some DBSFL did meet label guarantees. Five of the DBSFL samples analyzed did not meet crude protein label guarantees and were, on average, 12% below the crude protein minimum guarantee. Calcium levels analyzed were also far below label guarantees for two of the fourteen imported samples. Phosphorus was below the label guarantees in 3 of the 14 imported DBSFL products. Several of the DBSFL products do not meet their claimed nutrient levels nor do they meet the US label regulatory requirements.

The level of ultra-trace minerals and heavy metals varied dramatically. In general, nickel, vanadium, cobalt, molybdenum, and beryllium were below the limit of detection for all samples. Similarly, very few samples had detectable levels of barium, boron, antimony, or chromium, and only one sample had detectable levels of mercury. In contrast, arsenic, cadmium, and lead were detected in all samples analyzed, with wide variation particularly in samples of Chinese origin. On average, arsenic was eight times higher in Chinese-sourced DBSFL compared to N. American DBSFL, with the highest level detected at 2,620 ppb. Cadmium was slightly higher in Chinese-sourced DBSFL. On average, lead was twenty-five times higher, with the highest level detected of 4,930 ppb. Due to the significant variation among samples of Chinese-sourced DBSFL, there was no statistical difference as compared to N. American DBSFL levels.

The primary route of lead exposure is from food (Liu et al., 2019), and thus the source of lead in the imported DBSFL in this study may be due to feedstock sourced from environments with high lead levels from previous exposure to paint, gasoline, plumbing materials, and volcanic activity. In fact, lead has been identified as a significant concern in Chinese food items, and is notably high in fruits, vegetables, and cereal grains (Liu et al., 2019) which are common feedstocks for BSFL. In contrast to imported DBSFL, DBSFL sourced from N. America contained much lower levels of lead, likely a reflection of low levels of lead found in cereal grains and other feedstocks that would be fed to BSFL, livestock and other production animals and in human diets (FDA, 2022).

Lead is a contaminant of concern for poultry. Dietary lead negatively impacts laying hen performance and health, in part because lead replaces calcium in bone (NRC, 2006). Dietary lead is deposited into egg yolk and egg albumin in a dose dependent response, thus consumption of dietary lead by laying hens may result in lead exposure by those consuming eggs from that flock. Young children are at the highest risk of lead exposure, resulting in severe health impacts including neurocognitive effects. As previously stated, lead is present in the environment, and it is unlikely that feed ingredients will be completely devoid of lead but minimizing these levels and therefore the risk of lead exposure should be a priority. In some cases, imported product contained 62% more lead than that of the US sourced product.

Arsenic levels were also dramatically higher in Chinese-sourced DBSFL with much lower levels seen in N. American-sourced DBSFL. Like lead, these levels do not reach upper limits for feed in the US (APPA, 2023) but are high enough to merit consideration of the impact on hen health and egg nutrition. Arsenic can be found in drinking water and agricultural crops, likely because of water-derived arsenic exposure. Chronic and acute arsenic exposure is associated with negative health impacts (NRC, 2006). Poultry exposed to arsenic via feed or water can result in eggs containing arsenic, and egg arsenic levels are linearly correlated with feed and water levels (NRC, 2006). As in the case of lead, it is unlikely that a feeding program for poultry will be devoid of this heavy metal due to its presence at low levels in many common foods and feedstocks (FDA, 2022), but minimizing these levels should be a priority.

As noted above, other ultra-trace minerals and heavy metals were higher in Chinese-sourced DBSFL, but the biological risk associated with these levels is less clear. The source of higher levels of these heavy metals in imported DBSFL is likely from feedstock, water sources, or both. BSFL are known to deposit minerals in their exoskeleton (Finke, 2013) and thus management of dietary intake is critical to ensure safety of the finished dried product for animal consumption.

This study illustrates several major concerns for imported DBSFL being offered in the US retail market. Many of the Chinese-sourced products did not have label guarantee information that is compliant with current US regulatory requirements, and several products had no identifiable source/country of origin as required by state and federal laws, nor did they meet the provided label guarantees.

Insects are a natural part of a chicken’s diet, and providing DBSFL as a supplemental food item can improve hen health and welfare (reviewed in Koutsos et al., 2023). However, it is clear that not all sources of DBSFL are similar. Many retail DBSFL products do not provide the necessary and required information to meet US regulatory requirements, or do not meet their claimed nutrient levels. Additionally, lead and arsenic levels in imported DBSFL were significantly higher that DBSFL grown in the USA. Findings may be limited due to the sample size, the limited number of BSFL growers in North America and may not represent all imported DBSFL. However, the high level of lead and arsenic in some import samples are concerning as it not only affects the health of backyard flocks and humans via consumption of eggs from backyard flocks but also has the potential to contaminate the environment. Furthermore, the maximum detection levels of lead, arsenic, cadmium and mercury should be set to 1000ppb, 1000ppb, 200ppb and 50 ppb, displayed in Fig. 1. Due to the large amount of variation in levels of heavy metals within imported DBSFL, closer monitoring of heavy metal profiles of DBSFL and labeling compliance for DBSFL, could help reduce the risk of exposure.

Fig. 1.

illustrates the average heavy metal levels of DBSFL of N. American origin (± SEM), DBSFL of Chinese origin (± SEM) and the recommended maximum level of detection for DBSFL.

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: It should be noted that Perdue is currently selling a dried black solider fly larvae product (DBSFL) under the Brand FlockLeader. Before entering the backyard chicken market with a black solider fly larvae product, Perdue evaluated the quality of different sources of DBSFL to determine key market differentiators and evaluate potential suppliers. Based on the data presented in this research note, including the mislabeling and concerning levels of heavy metals, Perdue felt the data warranted publication. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.